Bug 821942 - Add xpcshell reason codes to marVersionDowngrade.js and marWrongChannel.js. r=spohl

toolkit/mozapps/update/tests/unit_base_updater/xpcshell.ini

@@ -18,8 +18,10 @@ tail =
 [marStageSuccessPartial.js]
 [marVersionDowngrade.js]
 skip-if = os != 'win' && os != 'mac'
+reason = mar signing
 [marWrongChannel.js]
 skip-if = os != 'win' && os != 'mac'
+reason = mar signing
 [marStageFailurePartial.js]
 [marCallbackAppSuccessComplete_win.js]
 skip-if = os != 'win'