fixup! virt: Update aexpect.Tail + new unittests

Signed-off-by: Chris Evich <cevich@redhat.com>
virt: Fix aexpect pickling & add unittests

* There's no reason for sub.stdin/stdout to remain open after
  Spawn.__init__(), so we just close them.
* Spawn.close() is now waits for the server to exit before
  cleaning files.  Otherwise it could clean, then new ones
  could still be written.
* Fixed up new-style pickle-support methods
* Added basic pickle test for Spawn class

Signed-off-by: Chris Evich <cevich@redhat.com>