Description of problem:

Trying to add to some user a permission for a vm pool, e.g. userRole permission, fails with error message:

<fault>
<detail>
Permission [dataCenter|cluster|host|storageDomain|vm|vmpool|template.id] required for add
</detail>
<reason>Incomplete parameters</reason>
</fault>

Trying to add the same permission to a different entity, e.g. to a cluster, works fine.

Version-Release number of selected component (if applicable):
rhevm-4.0.2-0.2.rc1.el7ev.noarch

How reproducible:
always

Steps to Reproduce:
1. Create a vm pool.
2. Add a user to your system or just use user admin.
3. With api v4 try to add userRole permission to the user's permissions collection e.g.:

URL = https://{engine}/ovirt-engine/api/users/{user_id}/permissions
body:

<permission>
    <role href="/ovirt-engine/api/roles/00000000-0000-0000-0001-000000000001" id="00000000-0000-0000-0001-000000000001">
        <name>UserRole</name>
        <description>Standard User Role</description>
        <link href="/ovirt-engine/api/roles/00000000-0000-0000-0001-000000000001/permits" rel="permits"/>
        <administrative>false</administrative>
        <mutable>false</mutable>
    </role>
    <vm_pool href="/ovirt-engine/api/vmpools/{pool_id}" id="{pool_id}">....
    ...{full vm_pool xml}...
 </vm_pool>
</permission>

Actual results:
POST call fails with:

<fault>
<detail>
Permission [dataCenter|cluster|host|storageDomain|vm|vmpool|template.id] required for add
</detail>
<reason>Incomplete parameters</reason>
</fault>

Expected results:
permission is added to the user successfully 

Additional info:
No interesting information in engine.log