libxl: MigrateConfirm: Dont unlock virDomainObj in helper function

libxl: MigrateConfirm: Dont unlock virDomainObj in helper function

The libxlDomainMigrateConfirm3Params API locks and ref counts the associated
virDomainObj but relies on the helper function libxlDomainMigrationConfirm
to unlock the object. Unref'ing the object is not done in either function.
libxlDomainMigrationConfirm is also used by libxlDomainMigratePerform3Params
for p2p migration, but in that case the lock/ref and unref/unlock are
properly handled in the API entry point.

Remove the unlock from libxlDomainMigrationConfirm and adjust
libxlDomainMigrateConfirm3Params to properly unref/unlock the virDomainObj
on success and error paths.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>