Removing useless code.

A simple object of NetworkcacheClient class is already instantiated by
setUp method.

slapos/libnetworkcachetests.py

@@ -123,10 +123,7 @@ class TestNetworkcacheClient(LibNetworkCacheMixin):
       Without the private key file, it is not possible to create the 
       signature so it must 
     """
-    nc = NetworkcacheClient(
-                   shacache=self.shacache_url,
-                   shadir=self.shadir_url)
-    self.assertEquals('', nc._getSignatureString())
+    self.assertEquals('', self.nc._getSignatureString())
 
   def test_signature_creation_with_private_key_file(self):
     """