Improved logging when PermissionController package is missing.

For example, if it's not enabled for managed profiles, the message would now be:

7-13 20:46:38.308 16176 16205 E PermissionControllerManager: No PermissionController package (com.google.android.permissioncontroller) for user 11
07-13 20:46:38.311 22224 22224 E AndroidRuntime: FATAL EXCEPTION: main
07-13 20:46:38.311 22224 22224 E AndroidRuntime: Process: com.afwsamples.testdpc, PID: 22224
07-13 20:46:38.311 22224 22224 E AndroidRuntime: java.lang.RuntimeException: Unable to start receiver com.afwsamples.testdpc.DeviceAdminReceiver: java.lang.IllegalStateException: No PermissionController package (com.google.android.permissioncontroller) for user 11

Instead of:

07-13 18:07:19.887 26168 26168 E AndroidRuntime: FATAL EXCEPTION: main
07-13 18:07:19.887 26168 26168 E AndroidRuntime: Process: com.afwsamples.testdpc, PID: 26168
07-13 18:07:19.887 26168 26168 E AndroidRuntime: java.lang.RuntimeException: Unable to start receiver com.afwsamples.testdpc.DeviceAdminReceiver: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ComponentInfo android.content.pm.ResolveInfo.getComponentInfo()' on a null object reference

Bug: 161135695
Test: adb shell setprop persist.debug.user.package_whitelist_mode 1
Test: # then install the TestDPC
Change-Id: I8d27b59cd5b96735e1d5e22a341bf869158e278f