Extract VolumeManager interface

- Move code in EbsVolumeCustomizer to EbsVolumeManager
- Move EbsVolumeLiveTest to EbsVolumeManagerLiveTest
MarkLogicNode: remove unused volume config
MarkLogicNodeSshDriver: use VolumeManager interface

- Instead of EbsVolumeManager, use VolumeManager interface so will be
  able to generalise for Rackspace etc.
Move EbsVolumeCustomizer to brooklyn.location.volumes

- was previously in io.cloudsoft.marklogic.nodes
Merge pull request #49 from cloudsoft/feature/volumes-extract-interface

Volumes: extract interface