NFS client configuration for cinder

This change adds the NFS client configuration in the cinder_volume hosts,
necessary when using a netapp backend over NFS.
Add python-swiftclient to swift hosts

* Add python-swiftclient to repo_packages list
* Allows the use of swift client on swift hosts

Fixes #596
Merge pull request #628 from andymcc/swift_client

Add python-swiftclient to swift hosts
Merge pull request #563 from miguelgrinberg/nfs_client_config

NFS client configuration for cinder (fixes #506)