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
Change-Id: I8460df6d49b4115d52748faaa1bbfecad8b0b856
Test: http://go/forrest-run/L89900000952178961
diff --git a/tests/unittests/AndroidTest.xml b/tests/unittests/AndroidTest.xml
index 429e670..0fc41f1 100644
--- a/tests/unittests/AndroidTest.xml
+++ b/tests/unittests/AndroidTest.xml
@@ -21,6 +21,10 @@
     <option name="test-suite-tag" value="apct" />
     <option name="test-suite-tag" value="apct-instrumentation" />
+    <target_preparer class="">
+        <option name="force-root" value="true" />
+    </target_preparer>
     <target_preparer class="">
         <option name="cleanup-apks" value="true" />
         <option name="test-file-name" value="RemoteProvisionerUnitTests.apk" />
@@ -29,5 +33,6 @@
     <test class="" >
         <option name="package" value="" />
         <option name="runner" value="androidx.test.runner.AndroidJUnitRunner" />
+        <option name="test-filter-dir" value="/data/data/" />