…stall

Details:

* Added the '-n' option to 'sphinx-build' in order to get reference not found
  warnings printed.

* Resolved reference not found warnings. Notable changes:

  - Added class 'pywbem.NocaseDict' to the docs.
  - Added class 'pywbem.MOFWBEMConnection' to the docs, and to the 'pywbem'
    namespace.
  - Added class 'pywbem_mock.CIMNamespaceProvider' to the docs.
  - Moved class 'IterQueryInstancesReturn' that was defined in the scope of
    method 'pywbem.IterQueryInstances' to the 'pywbem' namespace, and added it
    to the docs.

* In 'docs/conf.py', added the main directory of the repo to the Python module
  search path, so the documentation can be built without having the pywbem
  package installed. This is useful for packaging the project as an RPM, for
  example.

* Changed the Intersphinx prefix 'py' from Python 2 to Python 3.

* Changed some uses of the Intersphinx prefix 'py3' to use 'py'.

Signed-off-by: Andreas Maier <andreas.r.maier@gmx.de>

Details:

* Some pywbem_mock submodules were missing the '__all__' variable. This caused
  all names defined in and imported into the submodule to become visible in
  the 'pywbem_mock' namespace, which is undesirable.
  Added '__all__' where missing, with only the intended public names.

* Fixed use of incorrectly imported names in unit tests, that were used
  from the 'pywbem_mock' namespace. Used them from their defining submodules.

* Added import of the 'config' submodule into the 'pywbem_mock' namespace,
  in order to make sure that it is impoirted only once wnd that config variables
  can be modified.

Signed-off-by: Andreas Maier <andreas.r.maier@gmx.de>