Extending IBMNAS driver to support NFS based GPFS storage system

Extending IBMNAS driver to support NFS based GPFS storage system

- Adds support for hardware platform "NAS based on IBM GPFS
  deployments".
- This will enable IBM GPFS-NFS based storage systems to be used
  as a backend in OpenStack environments.

Driver certification test results:
  https://bugs.launchpad.net/cinder/+bug/1358590

DocImpact

Needs an update in ibmnas driver documentation as this change
proposes a new configuration option (ibmnas_platform_type)
to cinder.conf

Change-Id: I09098341ca1948775166883e9b2290061fa6ed37
Implements: blueprint add-gpfs-nas-to-ibmnas