Test Runner: Command line sharding args override env. Previously ANGLE would error out when both the enviornment and the command line args are specified at the same time. Because the perf bots use both at once we need to handle the conflict in the same way as the prior test runner does. In this case the command line takes precedence over the environment. Bug: angleproject:5124 Change-Id: I1ba765b4e75759922bf9fe2db9f153cfc5995f85 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2489722 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>