Description of problem:
VM Live Migration Starting a VirtualMachineInstance migration postcopy [test_id:4747] should migrate using cluster level config for postcopy

{"component":"virt-launcher","kind":"","level":"info","msg":"Starting post copy mode for migration","name":"testvmi-2ldvf","namespace":"kubevirt-test-default1","pos":"live-migration-source.go:577","timestamp":"2022-01-07T10:26:36.433194Z","uid":"cb664df9-edee-44b1-a8d4-32aa345cac1d"} {"component":"virt-launcher","level":"error","msg":"internal error: unable to execute QEMU command 'migrate-start-postcopy': Postcopy must be started after migration has been started","pos":"qemuMonitorJSONCheckErrorFull:418","subcomponent":"libvirt","thread":"44","timestamp":"2022-01-07T10:26:36.433000Z"} {"component":"virt-launcher","kind":"","level":"error","msg":"failed to start post migration","name":"testvmi-2ldvf","namespace":"kubevirt-test-default1","pos":"live-migration-source.go:582","reason":"virError(Code=1, Domain=10, Message='internal error: unable to execute QEMU command 'migrate-start-postcopy': Postcopy must be started after migration has been started')","timestamp":"2022-01-07T10:26:36.433875Z","uid":"cb664df9-edee-44b1-a8d4-32aa345cac1d"}

Version-Release number of selected component (if applicable):
4.9.2

How reproducible:
Hard to reproduce, Need to re-run the testcase multiple times to hit this error.

Steps to Reproduce:
1. update cluster-level config for postcopy
2. LiveMigrate a VM with "postcopy" migration.
3. VM fails to LiveMigrate.

Actual results:
reason":"virError(Code=1, Domain=10, Message='internal error: unable to execute QEMU command 'migrate-start-postcopy': Postcopy must be started after migration has been started')

"msg":"internal error: unable to execute QEMU command 'migrate-start-postcopy': Postcopy must be started after migration has been started"

Expected results:

Migration with postcopy is always successful

Additional info: