hotplug/Linux: close lockfd after lock attempt

hotplug/Linux: close lockfd after lock attempt

When a HVM guest is shutdown some of the 'remove' events can not claim
the lock for some reason. Instead they try to grab the lock in a busy
loop, until udev reaps the xen-hotplug-cleanup helper.
After analyzing the resulting logfile its not obvious what the cause is.
The only explanation is that bash (?) gets confused if the same lockfd
is opened again and again. Closing it in each iteration seem to fix the
issue.

This was observed with sles11sp2 (bash 3.2) and 4.2 xend.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Campbell <Ian.campbell@citrix.com>
[ ijc -- added the comment ]
Committed-by: Ian Campbell <ian.campbell@citrix.com>