Documenation builds specify a version in doc/source/conf.py that is
used in appropriate places through out the documentation. Previously
this value had not been defined properly and documentation builds
failed. Retrieve the version info using pkg_resources and set it
properly.
Use openstack.common.version to consume the generated version information
for documentation. Additional, add a swiftclient.__version__ member which
will return the version of swiftclient being used.
Change-Id: I14f3abdf00da3f9ea7d0651efe76b08f69ddabae
