CA-155178: Remove squeeze_xen cache if domain disappear

If domains lived no longer than 5 seconds, it will have big opportunity to have cache in squeeze_xen and will not remove by xenstore watcher since this procedure runs every 5 seconds.

This code change is to add a auto clean function in make_host to let the cache cleanup itself.
Signed-off-by: Cheng Zhang <cheng.zhang@citrix.com>