Modified to provide backward compatibility.

The slapos.libnetworkcache == 0.2 does not provide the signature script.

So, it should not be used if such script is not available.

src/zc/buildout/testing.py

@@ -364,7 +364,11 @@ def buildoutSetUp(test):
     def create_signature_file_list(path,
                                    private_key_file='private.pem',
                                    certificate_file='public.pem'):
+        try:
           from slapos.signature import createPrivateKeyAndCertificateFile
+        except ImportError:
+          return private_key_file, certificate_file
+
         private_key_file = os.path.join(path, private_key_file)
         certificate_file = os.path.join(path, certificate_file)
         createPrivateKeyAndCertificateFile(certificate_file, private_key_file)