Add check if EC is supported for factory_Leds test

BUG=chrome-os-partner:775
TEST=Run factory_Leds test in Mario and ZGA:

In Mario, you should see an exception like this:
  TestNAError: Currently not supported embedded controllers: ITE, SMSC

In ZGA, you should not see an exception like above one.

Change-Id: I62eade39f8d6d4a988abc58eb7b3875e0d949967

Review URL: http://codereview.chromium.org/3331008
1 file changed