[autotest] Move get_sheriffs() from common_lib's to server's utils.

This function pulls from a section other than client, which means that
it can never be run on a DUT, and thus has no point in being in
common_lib, which is meant for code that can be shared between client
and server, although those lines are a bit blurred at the moment.

TEST=unit?
BUG=None

Change-Id: Id92e1b344ff590c01d185bcd70ca67d7dba77938
Reviewed-on: https://gerrit.chromium.org/gerrit/61323
Reviewed-by: Prashanth Balasubramanian <beeps@chromium.org>
Reviewed-by: Alex Miller <milleral@chromium.org>
Tested-by: Alex Miller <milleral@chromium.org>
Commit-Queue: Alex Miller <milleral@chromium.org>
3 files changed