use test app's data folder as filter directory

During a retry, test methods to be retried are written into a
file, pushed onto device and read by the test instrumentation
for execution.

The default location for such filter file is /data/local/tmp,
which is prohibited for access by system uid packages, such
as the system UI tests package.

This change uses the test app's data folder for filter: this
is not generally applicable for all the tests since root
permission is required, but it is a relatively safe assumption
in case of testing against system uid pakcages since it
implies userdebug build is being used.

Bug: 152001555
Fixes: 208473429
Test: http://go/forrest-run/L76200000952166377
Change-Id: Ifc268a1cdb94ff8e47b6bd323464deb28e0c20ea

packages/SystemUI/tests/AndroidTest.xml

@@ -18,12 +18,17 @@
         <option name="test-file-name" value="SystemUITests.apk" />
     </target_preparer>
 
+    <target_preparer class="com.android.tradefed.targetprep.RootTargetPreparer">
+        <option name="force-root" value="true" />
+    </target_preparer>
+
     <option name="test-suite-tag" value="apct" />
     <option name="test-suite-tag" value="framework-base-presubmit" />
     <option name="test-tag" value="SystemUITests" />
     <test class="com.android.tradefed.testtype.AndroidJUnitTest" >
         <option name="package" value="com.android.systemui.tests" />
         <option name="runner" value="android.testing.TestableInstrumentation" />
+        <option name="test-filter-dir" value="/data/data/com.android.systemui.tests" />
         <option name="hidden-api-checks" value="false"/>
     </test>
 </configuration>