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.
Merge pull request #1174 from sjcorbett/ssh-tool-reuse

SshMachineLocation reuses SshTools