Store PBM wsdl in the oslo.vmware git repository

Currently, Cinder stores the PBM WSDL files in its own repository
(see commit: 10c5c93925abe3d34c4430e0ed852d8358fb2353). Now that other
projects are leveraging SPBM, we need to provide them the ability
to directly access those WSDL files without having to store them or
referencing them.

This patch (strongly inspired by the patch mentioned above) adds two
utility APIs and unit tests for it:
- get_pbm_wsdl_location()
- get_vc_version()

Change-Id: I61abc5879e71a7f5e5f46d2ec88404923e0423d8
Merge "Store PBM wsdl in the oslo.vmware git repository"