Even though we do some checking it is not as thorough as it
should be. We already have virStoragePoolObjIsDuplicate but the
way we use it is a typical TOCTOU. Imagine two threads trying to
define two pools with the same name but different UUIDs. With the
current code neither of them finds a duplicate and thus proceed
to virStoragePoolObjAssignDef where only names are compared.
Therefore both threads succeed which is obviously wrong.

We should check for duplicates where we care for them.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>