use a predefined pool for keyspace ops
Obscure bug involving 'fake' keyspaces being visible

* A pool is spun up for each keyspace
* If a keyspace doesn't exist, but is 'used' (e.g. describe_..)
        then the pool is spun up
* This causes subsequent requests (after the pool is created)
        to fail, since the pool is dangling
* The solution is to use a predefined pool for all keyspace ops
        and to start this pool up if it doesn't exist
Merge branch 'master' of github.com:dieswaytoofast/erlang_cassandra

Conflicts:
	src/erlang_cassandra.app.src
	src/erlang_cassandra.erl