[test-webkitpy] Make more than two -v options to be also verbose.

Passing more than two -v arguments for the test-webkitpy script
turned off debug logging.

BUG=none

Review URL: https://codereview.chromium.org/564173003

git-svn-id: svn://svn.chromium.org/blink/trunk@182226 bbb929c8-8fbe-4397-9dbb-9b2b20218538