virDomainCreateXML: Don't remove persistent domains on error

virDomainCreateXML: Don't remove persistent domains on error

https://bugzilla.redhat.com/show_bug.cgi?id=871452

Okay, so we allow users to 'virsh create' an already existing
domain, providing completely different XML than the one stored in
Libvirt. Well, as long as name and UUID matches. However, in some
drivers the code that handles errors unconditionally removes the
domain that failed to start even though the domain might have
been persistent. Fortunately, the domain is removed just from the
internal list of domains and the config file is kept around.

Steps to reproduce:

1) virsh dumpxml $dom > /tmp/dom.xml
2) change XML so that it is still parse-able but won't boot, e.g.
change guest agent path to /foo/bar
3) virsh create /tmp/dom.xml
4) virsh dumpxml $dom
5) Observe "No such domain" error

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>