[krillin] ofono crashes if restarted without OFONO_RIL_DEVICE=mtk

This is being reported on krillin ( ubuntu-touch/rc-proposed/bq-aquaris.en #60 ). The installed version of ofono is:

1.12.bzr6900+15.04.20150702.3-0ubuntu1

If ofono is restarted on the device by a root user using the 'restart' command, and the environment variable OFONO_RIL_DEVICE=mtk is not passed as an argument. ofono will crash. Unfortunately, the stack trace isn't very useful, or I'd include the .crash file with this bug. I do see that an assertion has fired as I see g_assertion_message_expr () from libglib-2.0, but I can't see the location in ofono that triggered the assertion.

Note, this is a result of the OFONO environment variables being setup by the rild system upstart job. If ofono crashes, the environment variables are properly set for the newly spawned ofono. It's only in the manual restart case that this crash is triggered. As such, I'm setting it to Medium priority.