Fix test_migration_live throwing AttributeError.

This patch fixes test_migration_live, which currently throws
an AttributeError, because self.block_migration is undefined.

This patch sets self.block_migration = 'auto' and the minimum
microversion to 2.25, which is when the block_migration
kwarg for live_migrate_server can be set to auto, so that nova
can decide the value of block_migration during live migration [0].

[0] https://developer.openstack.org/api-ref/compute/?expanded=live-migrate-server-os-migratelive-action-detail

Change-Id: I82572d9418901070d6925723241e5aabe0aeae8d
1 file changed