Description of problem:
-----------------------
RHHI-V uses VDO for dedupe & compression functionality. On top of VDO, thin LVs are created. In this combination, we found a problem (BZ 1600156), where discards weren't passed down, because of vdo_discard_sector(size) is smaller than thinpool's. To avoid that RHHI deployment at cockpit made custom changes to VDO systemd unit file to have the following:
---
ExecStartPre=/bin/sh -c "echo 4096 > /sys/kvdo/max_discard_sectors"
---
in /usr/lib/systemd/system/vdo.service.

But as per VDO instructions, with kernel > 4.6 (i.e) RHEL 8 kernel && from VDO 6.2, VDO exposes the option 'maxDiscardSize' per VDO volume.

RHHI-V 1.8 will be using RHEL 8.2 hosts, with RHV 4.4, with VDO 6.2.z.
This change needs to be updated in cockpit-wizard and that's the reason for existence of this bug

Version-Release number of selected component (if applicable):
-------------------------------------------------------------
kmod-kvdo-6.2.2.117-64.el8.x86_64
vdo-6.2.2.117-13.el8.x86_64
Kernel - 4.18.0-187.el8.x86_64
cockpit-ovirt-dashboard-0.14.1-1.el8ev.noarch0

How reproducible:
-----------------
Always

Steps to Reproduce:
-------------------
1. Start with RHHI-V deployment with VDO

Actual results:
---------------
systemd unit file for VDO (/usr/lib/systemd/system/vdo.service) has the following:
---
ExecStartPre=/bin/sh -c "echo 4096 > /sys/kvdo/max_discard_sectors"
---

Expected results:
-----------------
VDO option maxDiscardSize should be used instead

Additional info:
----------------
To bring about this change 2 places needs change
1. gluster-ansible-infra : 
    change-1: Remove the lines that customizes systemd VDO unit file
    change-2: Update the VDO options set on the newly created VDO volume
    Add the new option - 'maxDiscardSize' in /etc/ansible/roles/gluster.infra/roles/backend_setup/tasks/vdo_create.yml

2. cockpit-wizard: to set up the new VDO option while creating.

1. gluster-ansible changes
---------------------------
1. Remove the line from '/etc/ansible/roles/gluster.infra/roles/backend_setup/tasks/main.yml'
<snip>
# When VDO is used, upon creation and activation of thinpools discard is not
# possible, because of the misaligned discard size between thinpool and VDO.
# Warning: kernel: device-mapper: thin: Data device (dm-N) max discard sectors
# smaller than a block: Disabling discard passdown. Is displayed.
# To overcome this, add command in service file to set
# /sys/kvdo/max_discard_sectors to 4096 and restart vdo service

- name: Update vdo service to set /sys/kvdo/max_discard_sectors to 4096
  blockinfile:
     path: /usr/lib/systemd/system/vdo.service
     insertbefore: '^ExecStart='
     marker: "#{mark} ANSIBLE MANAGED BLOCK - DO NOT EDIT THIS LINE"
     block: |
        ExecStartPre=/sbin/modprobe -a uds
        ExecStartPre=/sbin/modprobe -a kvdo
        ExecStartPre=/bin/sh -c "echo 4096 > /sys/kvdo/max_discard_sectors"
  when: gluster_infra_vdo is defined
  tags:
    - vdocreate
</snip>

update required
<snip>
- name: Update vdo service to set /sys/kvdo/max_discard_sectors to 4096
  blockinfile:
     path: /usr/lib/systemd/system/vdo.service
     insertbefore: '^ExecStart='
     marker: "#{mark} ANSIBLE MANAGED BLOCK - DO NOT EDIT THIS LINE"
     block: |
        ExecStartPre=/sbin/modprobe -a uds
        ExecStartPre=/sbin/modprobe -a kvdo
  when: gluster_infra_vdo is defined
  tags:
    - vdocreate
</snip>

2. Update the VDO option 'maxDiscardSize' in /etc/ansible/roles/gluster.infra/roles/backend_setup/tasks/vdo_create.yml

cockpit-wizard change
----------------------
Add a new VDO volume option --maxDiscardSize=16M when new VDO volume is created