Do not ignore stackdriver errors when calling alert.py explicitly.
Do not ignore stackdriver errors when calling alert.py explicitly.

Normally an error collecting stats should not be considered fatal to
an app.  But when the sole purpose of the app is to collect stats --
as is the case with alert.py when run with `--stackdriver` -- then
failing *is* appropriate.

Auditors: dhruv

Test plan:
None

Khan/alertlib