Fix is_manual_test for files with no file extension.

In http://crrev.com/2132273002, I made an assumption that all
files have a "." character, which is incorrect. This is a follow-up
fix for that mistake.

BUG=626740

Review-Url: https://codereview.chromium.org/2144343002
Cr-Commit-Position: refs/heads/master@{#405790}
2 files changed