Description of problem:
Storage domain discard_after_delete default value it true, should be false.

As to why the discard_after_delete value default value should be false, Yaniv K. explains it the best at the following link:
https://lists.ovirt.org/archives/list/users@ovirt.org/thread/DGZOZ267NCZHSOBMPDVPA6UKHIZDOBNS/

Also aside from Yaniv reason, this will also be annoying to the customer as he will fail to add storage domains if his backend storage does not support DAD.
So he will have to go to each storage domain and change the DAD to false.

This change was introduced at:
Date: Dec 27, 2018 
commit: https://gerrit.ovirt.org/#/c/96386/
build:  ovrit-engine 4.3.0-0.5.alpha1.el7.noarch

Version-Release number of selected component (if applicable):
4.3.0.4-0.1.el7

How reproducible:
100%

Steps to Reproduce:
1.Create a block(ISCSI/FC) storage domain via UI/REST

Actual results:
discard_after_delete is set to true by default.

Expected results:
discard_after_delete should be set to false by default.

Additional info:
Yaniv full quote:
"
The whole purpose of
discarding is to allow the underlying storage to reclaim unused space. But
usually there's no need for it - you've deleted a disk, but you'd like to
use this space for a different disk - there's no need to give it back to
the storage (imagine file deletion in file system).
It only makes sense when the underlying storage is thin provisioned and you
need the space.
Y.
"

SD add request via REST without discard_after_delete(to see default value):
<storage_domain>
    <name>sd2</name>
    <storage>
        <logical_units>
            <logical_unit id="360002ac0000000000000001900021f6b">
                <address>10.35.146.1</address>
                <port>3260</port>
                <target>iqn.2000-05.com.3pardata:20210002ac021f6b</target>
            </logical_unit>
        </logical_units>
        <override_luns>true</override_luns>
        <type>iscsi</type>
    </storage>
    <storage_format>v4</storage_format>
    <type>data</type>
    <host>
        <name>host_mixed_2</name>
    </host>
</storage_domain>

SD add response:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<storage_domain href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7" id="dc992065-33a9-4b1f-a11c-a0af519f71f7">
    <actions>
        <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/isattached" rel="isattached"/>
        <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/updateovfstore" rel="updateovfstore"/>
        <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/refreshluns" rel="refreshluns"/>
        <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/reduceluns" rel="reduceluns"/>
    </actions>
    <name>sd2</name>
    <description></description>
    <comment></comment>
    <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/storageconnections" rel="storageconnections"/>
    <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/permissions" rel="permissions"/>
    <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/templates" rel="templates"/>
    <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/vms" rel="vms"/>
    <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/disksnapshots" rel="disksnapshots"/>
    <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/diskprofiles" rel="diskprofiles"/>
    <link href="/ovirt-engine/api/storagedomains/dc992065-33a9-4b1f-a11c-a0af519f71f7/disks" rel="disks"/>
    <available>47244640256</available>
    <backup>false</backup>
    <committed>0</committed>
    <critical_space_action_blocker>5</critical_space_action_blocker>
    <discard_after_delete>true</discard_after_delete>
    <external_status>ok</external_status>
    <master>false</master>
    <status>unknown</status>
    <storage>
        <type>iscsi</type>
        <volume_group id="ZXyNtE-n9sl-kKZx-Qw7n-SBrG-XBpS-8ZlZOS">
            <logical_units>
                <logical_unit id="360002ac0000000000000001900021f6b">
                    <address>3par-iscsi-1.scl.lab.tlv.redhat.com</address>
                    <discard_max_size>16777216</discard_max_size>
                    <discard_zeroes_data>false</discard_zeroes_data>
                    <lun_mapping>14</lun_mapping>
                    <paths>0</paths>
                    <port>3260</port>
                    <portal>3par-iscsi-1.scl.lab.tlv.redhat.com:3260,21</portal>
                    <product_id>VV</product_id>
                    <serial>S3PARdataVV_CZ3836C3RB</serial>
                    <size>53687091200</size>
                    <storage_domain_id>dc992065-33a9-4b1f-a11c-a0af519f71f7</storage_domain_id>
                    <target>iqn.2000-05.com.3pardata:20210002ac021f6b</target>
                    <vendor_id>3PARdata</vendor_id>
                    <volume_group_id>ZXyNtE-n9sl-kKZx-Qw7n-SBrG-XBpS-8ZlZOS</volume_group_id>
                </logical_unit>
            </logical_units>
        </volume_group>
    </storage>
    <storage_format>v4</storage_format>
    <supports_discard>true</supports_discard>
    <supports_discard_zeroes_data>false</supports_discard_zeroes_data>
    <type>data</type>
    <used>5368709120</used>
    <warning_low_space_indicator>10</warning_low_space_indicator>
    <wipe_after_delete>false</wipe_after_delete>
</storage_domain>