Manifest has several instrumentation, avoid the conflict

Explicitly specify the instrumentation runner to avoid
the wrong runner being used.

Test: atest android.content.cts.ContextTest -v
Merged-In: Ice3e45c1e4d0c2c8fa6ca2e761b38a2a0f555f1f
(cherry pick from master)

Change-Id: I7c5ce8c16f721c46bd1b93b9126d3fb173222644
diff --git a/tests/tests/content/AndroidTest.xml b/tests/tests/content/AndroidTest.xml
index 58305dd..4b22631 100644
--- a/tests/tests/content/AndroidTest.xml
+++ b/tests/tests/content/AndroidTest.xml
@@ -35,6 +35,7 @@
     </target_preparer>
 
     <test class="com.android.tradefed.testtype.AndroidJUnitTest" >
+        <option name="runner" value="android.support.test.runner.AndroidJUnitRunner" />
         <option name="package" value="android.content.cts" />
         <option name="runtime-hint" value="21m30s" />
         <option name="hidden-api-checks" value="false" />