test: ignore "Not Found: /tmp/.../zc.buildout" messages in doctests

Instead of using ellipsys use buildout provided way of ignoring these
messages.

slapos/recipe/cmmi/README.txt

@@ -324,10 +324,6 @@ default build options.
     configure --prefix=/sample_buildout/parts/package
     building package
     installing package
-    ...
-    ...
-    ...
-    ...
     <BLANKLINE>
 
 Check option "promises"

slapos/recipe/cmmi/tests.py

@@ -330,6 +330,7 @@ def test_suite():
                 (re.compile('\s/\S+sample-buildout'),
                  ' /sample_buildout'),
                 zc.buildout.testing.normalize_path,
+                zc.buildout.testing.not_found,
             ]),
         ),
         unittest.makeSuite(NonInformativeTests),