[Telemetry] Set run_tests default log level to WARN.
[Telemetry] Set run_tests default log level to WARN.

This is so that test skipped messages will show by default.

BUG=243874
TEST=tools/telemetry/run_tests --browser=android-content-shell BrowserTest
NOTRY=True

Review URL: https://chromiumcodereview.appspot.com/15796010

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@202174 0039d316-1c4b-4281-b951-d872f2087c98

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