qga: Add log to guest-fsfreeze-thaw command

Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

Jira: https://issues.redhat.com/browse/RHEL-56340

Signed-off-by: Dehan Meng demeng@redhat.com