xen 4.4.0 unnecessary dependency on Perl

[Anthony Wright <anthony@overnetdata.com>]

The shell script tools/hotplug/Linux/locking.sh contains a single
section of 8 lines of perl that causes xen 4.4.0 to be dependent on
perl, something that isn't mentioned anywhere in the documentation. The
section of code is trying to deal with a race condition and is
accompanied by the comment "Perl is very fast so use that".

To me it would seem wise to minimise the number of xen's dependencies
and so use Python instead or if speed is really important here, a custom
C program. We have a custom Linux distro that includes xen and to us the
size of the distro is very important. This single 8 line section of code
introduces a dependency on Perl and so adds another 10M to 20M.

Anthony.