Move some NetworkStats tests to tests/net.

This groups them together with the rest of the networking unit
tests. It also speeds up compile/test cycles ("runtest -x" of one
file goes from 1m15s to 30s).

Bug: 33681750
Test: runtest frameworks-net passes on internal tree
Merged-In: I53cb0c51355fe4b4b30e451fa09fbbf58da39efd
Change-Id: I5ae5dbf74c94feb0fe3759681e5e6d6fba62fa32

(cherry picked from commit c86013be936f36c61fa0cdfad95141f6de3c6ef7)

tests/net/java/android/net/NetworkStatsHistoryTest.java

@@ -38,7 +38,7 @@ import android.test.suitebuilder.annotation.SmallTest;
 import android.test.suitebuilder.annotation.Suppress;
 import android.util.Log;
 
-import com.android.frameworks.coretests.R;
+import com.android.frameworks.tests.net.R;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;

tests/net/java/com/android/internal/net/NetworkStatsFactoryTest.java

@@ -30,7 +30,7 @@ import android.net.NetworkStats;
 import android.net.TrafficStats;
 import android.test.AndroidTestCase;
 
-import com.android.frameworks.coretests.R;
+import com.android.frameworks.tests.net.R;
 
 import java.io.File;
 import java.io.FileOutputStream;