Add FLAG_IMMUTABLE flag to PendingIntent. It is required to specify the PendingIntent mutability flag strart from Android S. Bug: 178086680 Test: atest CtsAppTestCases:android.app.cts.ServiceTest#testForegroundService_pendingIntentForeground Change-Id: I51b67e07d6c04afe3a93d559eaccb0627c224c7e