Bug 861725 - Part 2: Revise the call forwarding test cases. r=vicamo

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rename : dom/mobileconnection/tests/marionette/test_mobile_call_forwarding_get.js => dom/mobileconnection/tests/marionette/test_mobile_call_forwarding_get_error.js
rename : dom/mobileconnection/tests/marionette/test_mobile_call_forwarding_set.js => dom/mobileconnection/tests/marionette/test_mobile_call_forwarding_set_error.js