Fixed the assert messages.

After merging the master branch inside the signature branch of
slapos.libnetworkcache it is required to fix some error messages.

src/zc/buildout/networkcache.txt

@@ -10,7 +10,11 @@ Pure buildout ignore networkcache:
    ... networkcache-section = networkcache
    ... ''')
    >>> print system(buildout)
-   Unused options for buildout: 'networkcache-section'.
+   While:
+     Initializing.
+     Getting section networkcache.
+   Error: The referenced section, 'networkcache', was not defined.
+   <BLANKLINE>
 
 So lets activate networkcache in buildout:
    >>> write(sample_buildout, 'buildout.cfg',
@@ -222,13 +226,13 @@ In case if download cache is failing, original resources are used:
    Installing eggs.
    Getting distribution for 'demo'.
    Downloading demo-0.4c1-py2.7.egg from network cache.
-   Failed to download from network cache demo-0.4c1-py2.7.egg: [Errno 111] Connection refused
+   Failed to download from network cache demo-0.4c1-py2.7.egg: <urlopen error [Errno 111] Connection refused>
    Uploading http://localhost/demo-0.4c1-py2.7.egg into network cache.
    Fail to upload file. [Errno 111] Connection refused
    Got demo 0.4c1.
    Getting distribution for 'demoneeded'.
    Downloading demoneeded-1.2c1.zip from network cache.
-   Failed to download from network cache demoneeded-1.2c1.zip: [Errno 111] Connection refused
+   Failed to download from network cache demoneeded-1.2c1.zip: <urlopen error [Errno 111] Connection refused>
    Uploading http://localhost/demoneeded-1.2c1.zip into network cache.
    Fail to upload file. [Errno 111] Connection refused
    Got demoneeded 1.2c1.