devserver.py: Move DevServerHTTPError from common_util to devserver.py

There is no other use case for this error class except in devserver.py
itself. This is causing some issues with importing cherrypy, etc. in
chromite. So its better to be here.

BUG=chromium:1025057
TEST=devserver_integration_test.py

Change-Id: Icf08ac60e2a78dacf54cac808abdcdebdc4aa675
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/1919646
Tested-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed