Handle cache mechanism when finding dataspaces

Previous findSpace function could return a dataspace from cache but would return a connection to the last active dataspace (current_space_). So, when looking for two spaces A and B, then A again, second A would return data from space B.

This is a quick fix by setting the current_space_ when necessary. As mentionned in the TODO, better fix would be to maintain all prepared statements per-schemas rather than globally.