Paygen: Split up Paygen into Build + Test stages.

Paygen was one giant stage.  Don had done some of the work to split out
the signer portion into its own stage.  This commit aims to split out
the testing portion into its own stage.

I call it, PaygenTest.  This stage essentially just schedules payload
tests and waits for the results.  The test payloads and artifacts are
created as part of the PaygenBuild stage and the PaygenTest stage is not
created until the artifacts are uploaded to GS.

The PaygenBuild and PaygenTest stages will be child stages of the Paygen
stage.

This will also be helpful in distinguishing failures with the actual
payload generation and those of the results from testing (or trying to
in some cases).

BUG=chromium:588282
BRANCH=None
TEST=python release_stages_unittest
TEST=python paygen_build_lib_unittest --network
TEST=payload tests tryjob

Change-Id: I4eafbd019af2c880adacaefa66bcdf393a60a1f7
Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Reviewed-on: https://chromium-review.googlesource.com/388922
Commit-Ready: Aseda Aboagye <aaboagye@chromium.org>
Tested-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
4 files changed