Bug 927139 - Expand automated coverage around keyboard usage when compos...

...ing a MMS message
I think this link to moztrap testcase should be moved to [test_sms_contact.py][link]
[link]:https://github.com/mozilla-b2g/gaia/blob/master/tests/python/gaia-ui-tests/gaiatest/tests/functional/messages/test_sms_add_contact.py#L16