Mark flaky battery-status tests in TestExpectations

TBR=timvolodine@chromium.org
BUG=384396

Review URL: https://codereview.chromium.org/343683003

git-svn-id: svn://svn.chromium.org/blink/trunk@176450 bbb929c8-8fbe-4397-9dbb-9b2b20218538