Allow using runtest with frameworks-services tests

Specifying a runner allows developers to run commands like:

`runtest frameworks-services`

without getting a message like:

"Could not find instrumentation
com.android.frameworks.servicestests/android.test.InstrumentationTestRunner
on device."

Bug: 28833951
Change-Id: I76fb58a8fa16db503c8e98eb5a09c481d41e0a76
Test: Described above
diff --git a/testrunner/test_defs.xml b/testrunner/test_defs.xml
index 46ed2ab..d475889 100644
--- a/testrunner/test_defs.xml
+++ b/testrunner/test_defs.xml
@@ -64,6 +64,7 @@
 <test name="frameworks-services"
     build_path="frameworks/base/services/tests/servicestests"
     package="com.android.frameworks.servicestests"
+    runner="android.support.test.runner.AndroidJUnitRunner"
     coverage_target="framework"
     continuous="true" />