Add SignatureTest#testSignature to knownfailures - temporarily

Bug: 17894722
Change-Id: I054c33c8dec15c3f4a88d9fc6c92b10068d1c890
diff --git a/tests/expectations/knownfailures.txt b/tests/expectations/knownfailures.txt
index 444d730..b4c9ebb 100644
--- a/tests/expectations/knownfailures.txt
+++ b/tests/expectations/knownfailures.txt
@@ -1,5 +1,12 @@
 [
 {
+  description: "signature test stil needs more work",
+  names: [
+    "android.signature.cts.SignatureTest#testSignature"
+  ],
+  bug: 17894722
+},
+{
   description: "Not all jdwp features are currently supported. These tests will fail",
   names: [
     "org.apache.harmony.jpda.tests.jdwp.DebuggerOnDemand.OnthrowDebuggerLaunchTest#testDebuggerLaunch001",