LU-11329 misc: populate MAINTAINERS file

LU-11329 misc: populate MAINTAINERS file

Add a relatively comprehensive set of subsystems to the MAINTAINERS
file, and assign patch reviewers to most of them.  There is room
for improvement, but at least this gives someone a chance to find
a maintainer for most of the code.

Update the get_maintainers.pl script to allow reading from stdin.
This allows the script to accept input from "git show <patch>"
to find reviewers for an existing patch.

Create a .mailmap file to map old email addresses to a fairly
current list of users (for now at least).  This allows
get_maintainers.pl to combine contributors into a single identity,
to avoid their "score" from being diluted across two identities.

Some addresses were not mapped from @whamcloud.com to @intel.com,
because they moved back to the @whamcloud.com domain again.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I12d223b4e1d4841c2b6fe1da65e69cd0bb4ebbe5
Reviewed-on: https://review.whamcloud.com/33413
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Emoly Liu <emoly@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>