[authfs][test] Use static fields from AuthFsTestRule in tests

This CL uses static fields from AuthFsTestRule directly instead
of redefining them in AuthFsHostTest.

Test: atest AuthFsHostTest
Change-Id: I5dd1d712598dbec702cd0cd8e8c8975c69b85655
diff --git a/authfs/tests/hosttests/java/src/com/android/fs/AuthFsHostTest.java b/authfs/tests/hosttests/java/src/com/android/fs/AuthFsHostTest.java
index 967d104..440f5ca 100644
--- a/authfs/tests/hosttests/java/src/com/android/fs/AuthFsHostTest.java
+++ b/authfs/tests/hosttests/java/src/com/android/fs/AuthFsHostTest.java
@@ -45,10 +45,10 @@
 public final class AuthFsHostTest extends BaseHostJUnit4Test {
 
     /** Test directory on Android where data are located */
-    private static final String TEST_DIR = "/data/local/tmp/authfs";
+    private static final String TEST_DIR = AuthFsTestRule.TEST_DIR;
 
     /** Output directory where the test can generate output on Android */
-    private static final String TEST_OUTPUT_DIR = "/data/local/tmp/authfs/output_dir";
+    private static final String TEST_OUTPUT_DIR = AuthFsTestRule.TEST_OUTPUT_DIR;
 
     /** Path to fsverity on Android */
     private static final String FSVERITY_BIN = "/data/local/tmp/fsverity";