Resolve a couple of memory leaks

Resolve a couple of memory leaks

Commit id '4b75237f' seems to have triggered Coverity into finding
at least one memory leak in xen_xl.c for error path for cleanup where
the listenAddr would be leaked. Reviewing other callers, it seems that
qemu_parse_command.c would have the same issue, so just it too.

(cherry picked from commit 727a3c5860ef5e1fb8878da9d44c6e5e33a4f4ae)