Add periodic node discovery with optional filters

Add support for periodic node discovery via system.peers.
Pass by HostInfo instead of the peer address

Pass the full HostInfo to the connection pool after getting new
hosts, with the caveat that seed hosts wont have valid host info.
remove SimplePool.newConn
Log errors when describing the ring
Fail fast if no seeds are available
Only set the hosts if the ring describer didnt error
Merge remote-tracking branch 'Zariel/cluster-ring-discovery' into cluster-ring-discovery
Introduce expectation for the cluster size
Set the discover hosts flag when trying to discover hosts
Merge MASTER into cluster-ring-discovery
clusterSize flag is actually a pointer
merge upstream/master
Use first provided host
Wait for the pool to settle
Make pause for autodiscovery configurable via a flag
Disable autodiscovery tests for Cassandra 1.2.x
Still getting a pool size of 2; should we wait much longer?
Must specify time unit when using test flag
Format the default value of a duration flag in a better way (Go is not very typesafe)
Using the wrong unit in time.Sleep() appears to send Go to sleep for quite a while