adds support for configuration of cinder nfs backend driver

a new config options is added: CONFIG_CINDER_NFS_MOUNTS , also adds
validate_multi_regepx for use with both NFS mounts and GlusterFS mounts

Change-Id: I5cf0ef0114c7eaa0bedd8528e6b1fe805221443a
Merge "adds support for configuration of cinder nfs backend driver"