Add init scripts for the metrics package

We are moving the init scripts out of chromeos-init
and into metrics/init.

BUG=chromium:346444
TEST=cbuildbot on x86-alex-paladin
CQ-DEPEND=CL:187455, CL:187470

Change-Id: If226addfaa154794361d3cf9687ca336b95b3104
Reviewed-on: https://chromium-review.googlesource.com/187456


Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>