Add more iterations to BuildDoc coverage.

Using testscenarios, construct more combinations of test options for
the autodoc_index_module option.

Change-Id: I96b2816be2c652478b37c03cb5755a83dfeb0894
Reviewed-on: https://review.openstack.org/25825
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins
Support forcing single-version-externally-managed.

git-review needs this to enable manpage installation.

Change-Id: I23ffc654fb2a83319c8d450e91304ae9ed767820
Reviewed-on: https://review.openstack.org/26283
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins