acouchbase - allow for async Admin connection

In order to incorporate the management API into acouchbase, the Admin connection needs to be asynchronous. While the implementation is straight-forward, due to PYCBC-866 (dependent upon CCBC-1204) some changes needed to be made on when the server version is obtained. The change is needed because the current HTTP request is within a synchronous path. Once the Admin connection becomes asynchronous this will no longer be viable (note this only impacts the acouchbase and txcouchbase APIs). The update is to obtain the server version within the C-bindings right after bootstrapping is complete (that way we know we have a valid lcb instance).

NOTE
The async Admin connection will be implemented for txcouchbase at a later date. The changes made with this ticket lay the ground work for future implementation and do not impact the use of the txcoucbhase API.