Set user.dir property when running CTS tests.

Some core library tests depend on this property being set. Notably the ones
that rely on the File(String path) behavior of using user.dir as the root path
when 'path' argument is a relative path.

Change-Id: I523c18868c7a3dd881743bca6ec867dad2361068
diff --git a/tests/core/runner/src/android/test/InstrumentationCtsTestRunner.java b/tests/core/runner/src/android/test/InstrumentationCtsTestRunner.java
index b5f1919..21eb2a6 100644
--- a/tests/core/runner/src/android/test/InstrumentationCtsTestRunner.java
+++ b/tests/core/runner/src/android/test/InstrumentationCtsTestRunner.java
@@ -87,6 +87,7 @@
         System.setProperty("java.home", cacheDir.getAbsolutePath());
         System.setProperty("user.home", cacheDir.getAbsolutePath());
         System.setProperty("java.io.tmpdir", cacheDir.getAbsolutePath());
+        System.setProperty("user.dir", cacheDir.getAbsolutePath());
         System.setProperty("javax.net.ssl.trustStore",
                 "/etc/security/cacerts.bks");