VMware vSphere support

(*) Copied the following utility files to execute vSphere queries from
'cinder'. These common utility files are going to be converted to a
library as a part of blueprint 'vmware-api' but till then these files
will be used as it is.

   api.py,
   error_util.py,
   vim.py,
   vim_util.py

(*) Using the above mentioned utilities, implemented a wrapper class for
querying performance stats from VC.

Change-Id: I445bcdb3f8ac240d1799bfd31f8b888982d7d97f
Implements: blueprint vmware-vcenter-server
(cherry picked from commit 026ee0145e1bcab19dbdd3cb2952d4c1e3d12634)

Conflicts:

	ceilometer/compute/virt/vmware/vsphere_operations.py
	ceilometer/tests/compute/virt/vmware/test_vsphere_operations.py

Change-Id: I51a7af37592393695ffd45d98cf2c647283d692b