Commit 19f8c980 introduced VIR_DOMAIN_UNDEFINE_SNAPSHOTS_METADATA,
with the intent that omitting the flag makes undefine fail, and
including the flag deletes metadata.  But it used the wrong logic.
Also, hoist the transient domain sooner, so that we don't
accidentally remove metadata of a transient domain.

* src/qemu/qemu_driver.c (qemuDomainUndefineFlags): Check correct
flag value.