This commit fixes a few things in the tempest docs. First it fixes all
of the sphinx warnings and enables fail on warn to ensure we're using
valid sphinx everywhere. It also adds a link from the configuration
guide to the sample config file.
Change-Id: I3ad645a6bbfa46b4498e1732410743e46d6eb0cb
Added docstring to cmd/account_generator.py.
Fixed help messages.
Added sphinx documentation for tempest-account-generator utility.
Change-Id: I6640ba8a0eaaea187cf38582ab537394dec020b6