bzip SELinux policy modules in ${datadir}

The 'semodule' utility can operate on compresed modules so the only
cost of this change is a slower module load time when invoking
'semodule -i' on a running system (increased CPU load due to bzip2).
That said my tests show more than 100M reduction in ext3 image size
of core-image-selinux. This last metric is a bit skewed as the image
includes two policies. Still, a reduction in the size of the refpolicy
package by 1/2 is significant.

Signed-off-by: Philip Tricca <flihp@twobit.us>