Tweak the messages so that they mention "title" rather than
"description" when operating in title mode. Also fixes one missing "%s"
before non-formatted gettext message.

Before:
 $ virsh desc --title dom
 No description for domain: dom

After:
 $ virsh desc --title dom
 No title for domain: dom

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1140034