findmissing: Add gerrit auth by passing cookies

Requested access for the GCE robot account to upload changes to
Gerrit (crbug/1054246).

The robot account gets access to Gerrit by passing in generated cookies to
each request. The gerrit-review URL is also modified to allow for GAIA
authentication by suffixing /a/.

BUG=None
TEST=ran functions to see if authorized + response returned

Change-Id: Ie9c4ef56e1832b93a40ed9a2b46e39ceedcc1ffc
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2097346
Reviewed-by: Curtis Malainey <cujomalainey@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Tested-by: Hirthanan Subenderan <hirthanan@google.com>
Commit-Queue: Hirthanan Subenderan <hirthanan@google.com>
3 files changed