Show how networkcache is installed.

src/zc/buildout/networkcache.txt

@@ -28,7 +28,10 @@ So lets activate networkcache in buildout:
    ...   slapos.libnetworkcache
    ...   zc.buildout
    ... ''')
-   >>> ignored = system(buildout)
+   >>> print system(buildout)
+   Installing networkcache.
+   Getting distribution for 'slapos.libnetworkcache'.
+   Got slapos.libnetworkcache ...
 
 Lets check that networkcache is correclty installed:
    >>> write(sample_buildout, 'buildout.cfg',