The virDomainDeviceInfoIsSet API was only checking if an
address or alias was set in the struct. Thus if only a
rom bar setting / filename, boot index, or USB master
value was set, they could be accidentally dropped when
formatting XML
(cherry picked from commit 2c195fdb)

Conflicts:

	src/conf/domain_conf.c

(crobinso: some elements aren't in maint branch, drop them)