Single digit MMI codes cause CTS to fail

Single digit MMI codes are invalid. These result in a notification
which interferes with UI tests during CTS. Turning this notification
into a toast message for when a single digit MMI code is dialed from
idle. Note that single digit codes are valid from within a call.

Change-Id: I9aa239d38573d070c9b7a8f86424a99162ddd57e
Issue-Id: FEIJ-142