Make kernel-install invocation non-fatal

Failing at this point will only result in untracked files all over
the system. Make it the administrator's responsibility to make sure
kernels are installed properly before re-starting.
Update (added GPIO beeper support)
Switch kernel & initrd compression from LZO to XZ

This pulls XZ decompression support into the kernel, while LZO
cannot be removed because of ZCACHE/FRONTSWAP.

Oh well. My /boot is filling up.
No reason to use a pseudonymous e-mail address
Un-mask gcc 4.9-scm
Mask gcc-4.9-scm as scm
Remove redundant sys-boot/dracut-scm