8281: Fix KeepClient retry bugs.

8281: Fix KeepClient retry bugs.

get() and put() were both handling all Curl exceptions -- including
timeouts -- by marking the keep service as unusable. For example, if a
single proxy is the only service available, a single timeout was
fatal. This is fixed by setting the retry loop status to None instead
of False after curl exceptions.

put() was repeating its retry loop until it achieved the desired
number of replicas _in a single iteration_. For example, when trying
to store 2 replicas, 6 loop iterations with a single success in each
iteration would result in 6 copies being stored but put() declaring
failure. This is fixed by checking against a cumulative "done" counter
instead of the "copies done in this loop iteration" counter.