Log more meaningful log DPMS isCredentialManagemenApp

* Differentiate logging error message when caller is
  not the credential management app and when the alias
  is not found in the authentication policy.

Bug: 177979648
Test: atest com.android.server.devicepolicy.DevicePolicyManagerTest
      atest android.security.CredentialManagementAppTest
      atest android.devicepolicy.cts.CredentialManagementAppTest
Change-Id: I31a95eb58637cb33522d48eaaef971ff13721a89