Fixing findVolumeSet return error

findVolumeSet was returning a dict instead of a str. This is
now fixed.

The documentation for findVolumeSet and findAllVolumeSets was
also updated to give more detail on what each method returns.

Added new unit tests for findVolumeSet.

Change-Id: Ia85134a306ef88618f610450a905520de7d9c961
Merge "Fixing findVolumeSet return error"
Fixing some doc errors for 3.1.2 client

* Added a findAllVolumeSets() automethod call so documentation
  is generated for it.
* Revised changelog to be a little more descriptive.
* Fixed some typos in findVolumeSet and findAllVolumeSets
  documentation comments.

Change-Id: I075df3b6366b6a82c4e06267ea82454d44390f7c
Adding two new APIs for system and CPGs

* Added a getCPGAvailableSpace API
  This method returns info about a CPG's available space

* Added a getOverallSystemCapacity API
  This method returns system capacity information

Change-Id: I7b3bc0ba8d1a917a1772671e58d17c0c95e635e4