tests: ensure migration status isn't reported as failed

tests: ensure migration status isn't reported as failed

Various methods in the migration test call 'query_migrate' to fetch the
current status and then access a particular field. Almost all of these
cases expect the migration to be in a non-failed state. In the case of
'wait_for_migration_pass' in particular, if the status is 'failed' then
it will get into an infinite loop. By validating that the status is
not 'failed' the test suite will assert rather than hang when getting
into an unexpected state.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220426160048.812266-10-berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>