Bug#616689: The bug now reaches the "separate /usr on lvm" case

[Raphael Plasson <rplasson@gmail.com>]

Few more informations,

I also met this bug on another computer, where both separate / and /usr
partitions were on lvm. I didn't have problem beforehand, but the
upgrade of initramfs-tools indeed lead to the same problem.
Interestingly, it is clear during the boot time that the lvm root
partition is correctly mounted, then initramfs waits for /usr, cannot
find it and fall back to initramfs prompt. "vgchange -ay" command and
exiting this prompt leads to a correct boot process. This time, I only
put a "lvm vgchange -ay" line on the lvm2 script, didn't specify any
kernel option to grub, and this solved the problem.

So as far as I can observe the problem on my computers:
- the problem only occurs for a separate /usr partition on lvm volumes
(no problem with / ): initramfs cannot find it
- a "lvm vgchange -ay" line on the
/usr/share/initramfs-tools/scripts/local-top/lvm2 added before the
"activate_vg" commands solves the problem (i.e. both / and /usr are
correctly found and mounted by initramfs)

-- Raphaël