backend: Log iso name in RunVmCommand

RunVmCommand now logs the name of attached iso, if any.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1034063
Change-Id: I6835d986b67c1dd457b14af8c948750c72e10ba8
Signed-off-by: Martin Betak <mbetak@redhat.com>