autotest: cellular: Raise error.TestFail instead of error.TestError.

The code seems to raise error.TestError where it should raise
error.TestFail. Fix this.

BUG=chromium:249162
TEST=Run network_CDMAActivate. If it fails it should only raise
TestFail.

Change-Id: I6ae84fe285a3c0f1d365b0a77e08230afb3434e7
Reviewed-on: https://gerrit.chromium.org/gerrit/58462
Reviewed-by: Thieu Le <thieule@chromium.org>
Commit-Queue: Arman Uguray <armansito@chromium.org>
Tested-by: Arman Uguray <armansito@chromium.org>
1 file changed