The 'docs' tox target executes the doc8 lint test which may result in
failures when testing documentation builds, but OpenStack-CI does not
execute that tox target.
In order to ensure that we catch all standard documentation syntax
errors and prevent them from merging, this patch includes the docs
target in the 'linters' chain of tests.
Fixes for any failures which result from executing this test are also
included in the patch.
Change-Id: I15e21908c9d453256220c304ce85f7488497e719
418ebd6e4b