tools/xendomains: Create lockfile on start unconditionally

tools/xendomains: Create lockfile on start unconditionally

At the moment, the xendomains init script will only create a lockfile
if when started, it actually does something -- either tries to restore
a previously saved domain as a result of XENDOMAINS_RESTORE, or tries
to create a domain as a result of XENDOMAINS_AUTO.

RedHat-based SYSV init systems try to only call "${SERVICE} shutdown"
on systems which actually have an actively running component; and they
use the existence of /var/lock/subsys/${SERVICE} to determine which
systems are running.

This means that at the moment, on RedHat-based SYSV systems (such as
CentOS 6), if you enable xendomains, and have XENDOMAINS_RESTORE set
to "true", but don't happen to start a VM, then your running VMs will
not be suspended on shutdown.

Since the lockfile doesn't really have any other effect than to
prevent duplicate starting, just create it unconditionally every time
we start the xendomains script.

The other option would have been to touch the lockfile if
XENDOMAINS_RESTORE was true regardless of whether there were any
domains to be restored.  But this would mean that if you started with
the xendomains script active but XENDOMAINS_RESTORE set to "false",
and then changed it to "true", then xendomains would still not run the
next time you shut down.  This seems to me to violate the principle of
least surprise.

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Olaf Hering <olaf@aepfle.de>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>