full_release_test.py: Handle delta payload file names on non-release builds

Non-release builds have a date fragment in the version file name. Handle
it as well.

Also fix assumptions about the source_uri for npo full updates.
Specifically, use the target version to find the full update
payload when source and targets are the same. This ensures the
logic correctly handles developer build version names (with the date).

BUG=chromium:425404
BUG=chromium:390828
TEST=New unit test
TEST=trybots on storm-release, storm-paladin, lumpy-release, lumpy-paladin

Change-Id: I3f5f454702269a93020d266eebc917966ea79ce8
Reviewed-on: https://chromium-review.googlesource.com/236675
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Gaurav Shah <gauravsh@chromium.org>
Tested-by: Gaurav Shah <gauravsh@chromium.org>
2 files changed