Specs were previously under doc/specs and where thus not being rendered
via the docs build process [1]. This patch moves the directory to
doc/source/specs so that'll happen now, and makes minor tweaks to the
documents themselves to clear build errors.
More work should be done at some point soon to split out the appropriate
parts of test-requirements.txt into a doc/requirements.txt.
[1] https://governance.openstack.org/tc/reference/project-testing-interface.html#documentation
Change-Id: I1e2eff09114ef2f2fca883adb454536fb39ab64d
d116a63414