Add support for devserver latestbuild RPC for Android build

Add a new request argument os_type to differentiate requests for android builds
and ChromeOS builds. The value needs to be set to `android` for any request
related to Android build. If the value is not set or has other values, default
to ChromeOS builds.

BUG=chromium:512668
TEST=run devserver locally, and
curl http://localhost:8082/stage?target=shamu-userdebug\&build_id=2040953\&artifacts=test_zip\&branch=git_mnc-release\&os_type=android
curl http://localhost:8082/latestbuild?target=shamu-userdebug\&branch=git_mnc-release\&os_type=android

Change-Id: I32dd118c7c03c5899742cebe437d34b9cef984de
Reviewed-on: https://chromium-review.googlesource.com/308755
Commit-Ready: Dan Shi <[email protected]>
Tested-by: Dan Shi <[email protected]>
Reviewed-by: Simran Basi <[email protected]>
2 files changed