WIP: Add test_util

The addition of start_config here is suboptimal, but starting couch
requires config to be running, and a number of the tests also want
config running, so this is a (temporary?) workaround to make sure you
can always get a fresh config instance.

Currently the request function is unused, but I think we should
migrate tests making requests to use it.
WIP: Switch to using test_util:start_config
WIP: Disable problematic tests
WIP: add couch_eunit.hrl
Update couch module tests for renamed config app
Remove couch_ref_counter from couch module tests
Rename couch_server_sup to couch_sup in couch module tests
Use mochiweb_http:stop instead of gen_server:cast(.., stop)

The version of mochiweb currently used does not support sending a cast
stop message, so use the builtin stop function.