Add attribute for ibm nas stroage driver ibmnas_platform_type

* Add new ibmnas_platform_type attribute
* Fix minor bug with nas_ssh_port

Change-Id: I147fbb75cf75357f578e4f84a0d898149be9b1d0
Closes-Bug: #1370574
Merge "Add attribute for ibm nas stroage driver ibmnas_platform_type"