Correct the path to authentication file.
Correct the path to authentication file.

Also print an error if it's not there.

BUG=skia:2571
R=borenet@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/308043004

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot