vmware: Refactor: fold volume_util.py into volumeops.py

volume_util.py seems to have originally been intended to be a general
repository of operations on volumes. In fact, it was an arbitrary
collection of iscsi functions which were exclusively called by
VMwareVolumeOps with VMwareVolumeOps private data as arguments.

This change moves all functions from volume_util.py into
VMwareVolumeOps in volumeops.py. This makes it simpler to read and
understand the code, as there is now only a single place to look for
iscsi functions. It also moves StorageError into volumeops.py, as that
is the only place it is used. Arguments have been updated to use
private data directly rather than having them passed in. In addition,
function names have been updated to accurately reflect their actual
purpose.

There are no functional changes. All code change is purely mechanical.

Change-Id: I17f4b71c0314e555d9f7dc1a935865865dd06c51
Merge "vmware: Refactor: fold volume_util.py into volumeops.py"