2.19 - Allow the user to set and get the server description. The user will
be able to set the description when creating, rebuilding, or updating
a server, and get the description as part of the server details.
Methods `rebuild` and `create` of novaclient.v2.servers.ServerManager were
not wrapped with `api_versions.wraps` decorator to reduce code and docsting
duplication. Version checks added inside these methods.
Change-Id: I75b804c6edd0cdf02c2cd002d0b5968fec8da545