Add CTS tests for DPM.getKeyPairGrants() Bug: 160457441 Test: atest com.android.cts.devicepolicy.MixedManagedProfileOwnerTest#testKeyManagement Test: atest com.android.cts.devicepolicy.MixedDeviceOwnerTest#testDelegatedCertInstallerDirectly Test: atest android.admin.cts.DevicePolicyManagerTest Change-Id: If47cb7774993647d056b97aa9cf200a6c9f2419a