LU-553 build: Lustre style commit hooks for Git

LU-553 build: Lustre style commit hooks for Git

Adds recommended commit hooks for Lustre commit messages, that
can/should be installed into lustre/.git/hooks for all Lustre trees.

prepare-commit-msg: adds the output of checkpatch.pl as a
    comment to the commit message, to "soft" validate the new
    patch is matching the Lustre coding style. It doesn't check
    100% of the Lustre coding style, but at least finds most of
    the obvious errors so that they can be fixed locally before
    any manual inspection time is spent on the patch.

commit-msg: verifies the format of the commit message (somewhat).
    Checks that there is a valid-looking Signed-off-by: line.
    Adds the Gerrit Change-Id: line for change tracking.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I35fdfb8206d1f0efb3bb401522e8412c62b7c02a
Reviewed-on: http://review.whamcloud.com/1296
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>