devserver: Basic healthchecks for devserver.

This CL provides some basic healthchecks for the
devserver for use with the Mob* Monitor. It
provides checks for:
 - ensuring a Boto key is present
 - ensuring we can access google storage

BUG=chromium:522196
TEST=Deployed and tested on a moblab.

Change-Id: I4543e1d47541d82cbaf0318382d89fa01f6a976c
Reviewed-on: https://chromium-review.googlesource.com/298608
Commit-Ready: Matthew Sartori <msartori@chromium.org>
Tested-by: Matthew Sartori <msartori@chromium.org>
Reviewed-by: Matthew Sartori <msartori@chromium.org>
2 files changed