tools/pygrub: remove /var/run/xend/boot from install target

tools/pygrub: remove /var/run/xend/boot from install target

pygrub stores the temporary kernel+initrd files in /var/run/pygrub, or
any other directory specified with --output-directory=<dir>. If the
default dir is missing pygrub will create it.

Without this change installing the resulting xen.rpm will fail on
systems where /var/run is a symlink. rpm complains that '/var/run' (the
symlink) is already owned by some other system rpm package.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>