Fix verify_counter_repl test, broken by other commits.

Fixes riak_test verify_counter_repl

Cause of failure was due to calling undefined functions, previously exported, but then hidden by recent commit:
https://github.com/basho/riak_test/commit/bc69a596361449ca7f3c03bd8394e4f916b2169b

Somebody, maybe with initials SC, didn't run the other tests after changing verify_counter_converge. Boo.

But in the spirit of improvement, the verify_counter_repl test now uses the new client support directly and is a cleaner test. Yay. On with pre4 testing.

@seancribbs as possible reviewer :-)