[buildout][develop] Add nose to list of eggs

Otherwise it's not taken into account when setting
up the development environment with buildout and
the statistics tests can't run properly as the django
script does not contain the path to the appropriate
egg.

develop.cfg

@@ -2,6 +2,7 @@
 extends = common.cfg
 always-checkout = force
 versions = versions
+eggs += nose
 develop = src/beat.backend.python
           src/beat.core
           src/beat.cmdline