Fix PackageSignatureTest#testPackageSignatures

Add android.core.tests.runner to the whitelist exception list.
This is just a package used while running CTS is not of concern.

Change-Id: I5212cb1336a029c228187731c08012a3a8940d72
diff --git a/tests/tests/security/src/android/security/cts/PackageSignatureTest.java b/tests/tests/security/src/android/security/cts/PackageSignatureTest.java
index 4dddd5d..3822035 100644
--- a/tests/tests/security/src/android/security/cts/PackageSignatureTest.java
+++ b/tests/tests/security/src/android/security/cts/PackageSignatureTest.java
@@ -80,7 +80,10 @@
             "android.deviceadmin.cts",
 
             // APK for an activity that collects information printed in the CTS report header
-            "android.tests.devicesetup"
+            "android.tests.devicesetup",
+
+            // APK for the Android core tests runner used only during CTS
+            "android.core.tests.runner"
             ));
 
     private boolean isWhitelistedPackage(String packageName) {