Tidies for readability and formatting in SshMachineLocation and related classes
Adds KeyTransformingLoadingCache to brooklyn-utils
Cache and reuse SshTools in SshMachineLocation.

* Uses LoadingCache to create, store and expire SshTool instances
* Properties in REUSABLE_SSH_PROPS are removed from Map given to
  connectSsh via BasicPool supplier.
Increases RedisStoreImpl sensor poll period to five seconds
Log exceptions thrown when closing SshTool pools.
Fix Cassandra fabric setting seeds
Reduce excessive cassandra-seed logging

- CassandraNode was repeatedly publishing serviceUp, causing log.debug
  every second
- Don't log on fabric stopping (otherwise complains no seeds, with
  scary threat of split-brain)
Merge pull request #1174 from sjcorbett/ssh-tool-reuse

SshMachineLocation reuses SshTools
Merge pull request #1176 from aledsage/fix/CassandraFabric-setting-seeds

Fix setting seeds in CassandraFabric