Default persistenceDir to ~/.brooklyn/

- Adds BrooklynConfigKeys.BROOKLYN_PERSISTENCE_DIR
- Default persistenceDir is ~/.brooklyn/brooklyn-persistence-state/data
- If CLI doesn't set --persistenceDir then use config key value
  from brooklynProperties
rebind: incorporate review comments
Merge pull request #1199 from aledsage/fix/persistenceDir

Default persistenceDir to ~/.brooklyn/