apparmor: Allow /usr/libexec for private xen-tools binaries

apparmor: Allow /usr/libexec for private xen-tools binaries

This is a followup for commit e906c4d02bdcddf141b4d124afd68c8ee10134fe
("apparmor: Allow /usr/libexec for libxl-save-helper and pygrub"):

In recent rpm versions --libexecdir changed from /usr/lib64 to
/usr/libexec. A plain rpmbuild %configure in xen.git will install all
files, including the private copies of qemu, into /usr/libexec/xen/bin.
Expand the existing pattern to cover also this libexecdir variant.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>