Fix boot-seed-vm/create-nodes for old e2fsprogs

Change Id7f999ea17c84ea61b733cf6d0b74c95fdae0413 introduced
an optimization of FS operations by means of "chattr +C" call.
Ubuntu 12.04 LTS ships e2fsprogs version, that doesn't support
+C option, so both boot-seed-vm and create-nodes scripts fail
on this step.

As it's just an optimization, we can add || true to chattr calls
to ensure boot-seed-vm and create-nodes still work with old
versions of e2fsprogs.

Fixes bug 1226570

Change-Id: I27e94de35b9655cc669b6845522834fc9bac381a