GitLab

Made all builders to use the task service account to access Goma.
I removed options from lib and made use_luci_auth=true mandatory.

Bug: crbug.com/1105814
Change-Id: I8c0dff203a96e34db0b5ec1ac79b70289e2ae9e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2411561Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806951}