Upgrade to non-realtime kernel resets default kernel to non-realtime on realtime system

Issue

• I have an MRG system running the kernel-rt realtime kernel. When I install an upgrade to the "kernel" package, the default boot kernel is reset to that new kernel, overriding the realtime kernel.

• The post-install for the kernel package should check to make sure that the default boot is actually using the kernel package before changing the default boot.