Fix bug where grouped builder points at wrong archive URL.
Fix bug where grouped builder points at wrong archive URL.

BUG=chromium:345346
TEST=Example remote trybot run with group and without group.

Change-Id: I0c8778b44da71f1f0c37388bd5bb1fa3fe6b652f
Reviewed-on: https://chromium-review.googlesource.com/187750
Reviewed-by: Matt Tennant <46e612415b446ccde19638e4035892001c237942@chromium.org>
Commit-Queue: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite