ONTAP plugin: Improve disk status and disk type query
* Fix a trivial problem when no volume/LUN.
* Improve disk type query by using 'effective-disk-type'.
NetApp allowing disks with the same 'effective-disk-type' to create
* Improve disk status.
* Tested in ONTAP simulator for all coded status except this:
# I cannot actually broke a disk in ONTAP simulator.
Changes in V2:
* Remove debug code(print) from ONTAP plugin.
* Hide non-public constants in ONTAP plugin.