Description of problem:

When one of our customers run `tempest.api.compute.admin.test_live_migration.LiveMigrationTest.test_live_block_migration_paused`, nova-compute.log in their compute node showed an error from tempest[1] and an error from libvirt driver in Nova.

On the other hand, when I checked the customer's sosreport, I found live_migration_permit_post_copy=True in nova.conf in their compute node. So, I think that this configuration caused these errors.

IMHO, I think that `test_live_block_migration_paused` should take into account `live_migration_permit_post_copy=True`

[1] message from tempest:
~~~

tempest.api.compute.admin.test_live_migration.LiveAutoBlockMigrationV225Test.test_live_block_migration_paused [20.953129s] ... FAILED

Captured traceback:
~~~~~~~~~~~~~~~~~~~
b'Traceback (most recent call last):'
b' File "/usr/lib/python3.6/site-packages/tempest/api/compute/admin/test_live_migration.py", line 153, in test_live_block_migration_paused'
b" self._test_live_migration(state='PAUSED')"
b' File "/usr/lib/python3.6/site-packages/tempest/api/compute/admin/test_live_migration.py", line 129, in _test_live_migration'
b' self._live_migrate(server_id, destination_host, state, volume_backed)'
b' File "/usr/lib/python3.6/site-packages/tempest/api/compute/admin/test_live_migration.py", line 94, in _live_migrate'
b' msg)'
b' File "/usr/lib/python3.6/site-packages/testtools/testcase.py", line 411, in assertEqual'
b' self.assertThat(observed, matcher, message)'
b' File "/usr/lib/python3.6/site-packages/testtools/testcase.py", line 498, in assertThat'
b' raise mismatch_error'
b"testtools.matchers._impl.MismatchError: 'rhosp-cmp12.xxxxxx' != 'rhosp-cmp10.xxxxxx': Live Migration failed. Migrations list for Instance d7dbcccc-692b-4de2-8d78-216e3d4e8018: ["
b"

]"
b''
~~~

[2] message from libvirt driver:
~~~
2022-02-04 10:16:54.266 7 ERROR nova.virt.libvirt.driver [-] [instance: c281705e-df31-480e-adad-f6650864e936] Live Migration failure: argument unsupported: post-copy migration is not supported with non-live or paused migration: libvirt.libvirtError: argument unsupported: post-copy migration is not supported with non-live or paused migration
~~~

Version-Release number of selected component (if applicable):

openstack-tempest-26.1.0-2.20210531080657.271f820.el8ost.1

How reproducible:

Always if live_migration_permit_post_copy is True in nova.conf in compute nodes.

Steps to Reproduce:
1. Set live_migration_permit_post_copy to True in nova.conf.
2. run the test tempest.api.compute.admin.test_live_migration.LiveAutoBlockMigrationV225Test.test_live_block_migration_paused

Actual results:

The test failed.

Expected results:

The test should be done successfully even if there is a setting `live_migration_permit_post_copy=True` in nova.conf.