Bug 842064: Fix build bustage caused by expired certificates in test_signed_apps.js on a CLOSED TREE, a=bustage, a=testonly

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extra : source : ff193fc3dc7d37db4081dd95f1f1aa8e3551d527
extra : histedit_source : 5b6de6aae72860b31173a4a7540f123ecae8892e