Keeping a single index pool per RS

Pools are cached by name in the RSCPHost#sharedData and accessed
in a thread-safe way through the ThreadPoolManager. We ensure uniquness
across servers by tagging on the RS name to the pool name. Its a little
ugly, but makes life easier with testing.
Merge pull request #462 from jyates/single-instance-pools-per-server

Keeping a single index pool per RS