[cbuild] Pass the Gerrit host to the api.gerrit call

The autodection in the recipe module doesn't work because there is no
input commit to detect the Gerrit host from. Therefore, it needs to be
passed to the function. The buildbucket.ci_build expectation provided an
input commit which made the tests pass but the actual runs fail with an
assertion error.

Change-Id: Ifc1bd79070a96433dfa52432b92e7c0d9de5cd84
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/165540
Auto-Submit: Alexander Thomas <athom@google.com>
Reviewed-by: Karl Klose <karlklose@google.com>
Commit-Queue: Karl Klose <karlklose@google.com>
3 files changed