[autotest] Offload crash handling to a dedicated server.

Add the ability to specify a dedicated devserver to handle
symbolicate_dump rpc calls to offload work from the main dev_server.

BUG=chromium-os:32710
TEST=unit

Change-Id: I11313a92a96709bbc0feeeaea1c755adb92a4290
Reviewed-on: https://gerrit.chromium.org/gerrit/27940
Tested-by: Alex Miller <milleral@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Ready: Alex Miller <milleral@chromium.org>
3 files changed