Static layout: support image verification

Add support of image verification for static layout PNOR code update.

Tested: Verify the PNOR code update succeeds with valid-signed PNOR;
        and fails with invalid-signed PNOR or a PNOR tarball without
        signature.

Change-Id: I1aafeb4e8e07eaa16c170f33f4f21940f7c9c146
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/test/test_signature.cpp b/test/test_signature.cpp
index b199c74..9e8de4b 100644
--- a/test/test_signature.cpp
+++ b/test/test_signature.cpp
@@ -82,7 +82,8 @@
         command(opensslCmd + pkeyFile + " -out " + pubkeyFile + ".sig " +
                 pubkeyFile);
 
-        signature = std::make_unique<Signature>(extractPath, signedConfPath);
+        signature = std::make_unique<Signature>(extractPath, "pnor.xz.squashfs",
+                                                signedConfPath);
     }
     virtual void TearDown()
     {