Allow to find slapos.libnetworkcache during test.

src/zc/buildout/testing.py

@@ -269,7 +269,7 @@ def make_buildout(executable=None):
     """Make a buildout that uses this version of zc.buildout."""
     # Create a basic buildout.cfg to avoid a warning from buildout.
     open('buildout.cfg', 'w').write(
-        "[buildout]\nparts =\n"
+        "[buildout]\nparts =\nfind-links = http://pypi.python.org/pypi/slapos.libnetworkcache"
         )
     # Get state of installer defaults so we can reinstate them (instantiating
     # a Buildout will force the Buildout's defaults on the installer).