Don't fail if vold.fstab doesn't exist.

Bug: 5014713
Change-Id: Iddd7837833599327982fd7a1371ecc4078e3af6e
diff --git a/tests/tests/security/src/android/security/cts/VoldExploitTest.java b/tests/tests/security/src/android/security/cts/VoldExploitTest.java
index 38eece7..12b4392 100644
--- a/tests/tests/security/src/android/security/cts/VoldExploitTest.java
+++ b/tests/tests/security/src/android/security/cts/VoldExploitTest.java
@@ -115,6 +115,9 @@
     private static Set<String> getSysFsPath(String file) throws IOException {
         Set<String> retval = new HashSet<String>();
         File netlink = new File(file);
+        if (!netlink.canRead()) {
+            return retval;
+        }
         Scanner scanner = null;
         try {
             scanner = new Scanner(netlink);