Update getCallerIdentityOptionalAdmin/Package

* if the admin/package is null, try get the active admin
  of the caller. If the active admin is found, create the
  calleridentity object with the adminComponent/package.
* If not active admin is found, create a calleridentity
  object, where the adminComponent/package is null.

Bug: 170095758
Test: atest com.android.server.devicepolicy.DevicePolicyManagerTest
Change-Id: I25ae367af3fa3013e800989e9e0acc1f85821bab