Bug#789150: #789150 boot failure with root=UUID= and software RAID

[Elliott Mitchell]

I ran into this issue myself and was trying to figure out how to solve
it.

Examining the initrd image which had been created, the
63-md-raid-arrays.rules and 64-md-raid-assembly.rules files were absent.
As mentioned in #789150, mdadm now has its own
/usr/share/initramfs-tools/hooks/mdadm which *should* copy those two
files into any initrd which is created.

When I regenerated the initrd by running `update-initramfs -u -k all`,
the two udev rules files *were* present.  Looking at things there are
two things I /suspect/ may have happened.

First, when initially building the image for this system I was working
from a qemu image.  Reliability was handled outside of qemu and hence the
mdadm package didn't include itself into the initrd.  Perhaps the mdadm
initramfs hook script should treat a value of "MODULES=most" as an
indicator to *always* include itself into the initrd (this IS a hint that
something major may change soon).

Second, perhaps the issue was the mdadm package was installed /after/
the kernel and bootloader packages were installed so the initial ramdisk
image was never rebuilt.  Perhaps this indicates mdadm's postinst script
needs to preemptively run `update-initramfs -u -k all` after
installation (similar situation for postrm).


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