Show ProgressDialog when waiting for radio to turn on when provisioning.

Turning on the cellular radio when user selects the provisioning notification
can take 30-60s so a UI is needed to keep the user informed that the radio is
coming up. This is only for provisioning APN support (only AT&T tablets now).

bug:15990642
Change-Id: Ibea894ee934bae2045c0462ae79bfa39d0ef3f05