Add caller check to

* Only the Settings app can reset credentials
* should still be
  callable by CertInstaller.

Manual testing steps:
* Install certificate via Settings
* Verify unable to reset certificates via test app
  provided in the bug (app-debug.apk)
* Verify able to reset certificates via Settings
* Verify isn't changed

Bug: 200164168
Test: manual
Change-Id: I9dfde586616d004befbee529f2ae842d22795065
(cherry picked from commit 4c1272a921bb9037e17a01e1e5a0692f7f704c3d)
Merged-In: I9dfde586616d004befbee529f2ae842d22795065
1 file changed