Change the dependency with the testenv:docs

Add the description for pep8, docs, pdf-docs, releasenotes, api-ref.
Change the pdf-docs and releasenotes's packages dependency with the
test docs requirement.

Story: 2008360

Change-Id: Ifcb28a340733b90329970be0078118d523b64bd3

tox.ini

@@ -88,6 +88,8 @@ ignore-path = .venv,.git,.tox,*cyborg/locale*,*lib/python*,*cyborg.egg*,api-ref/
 
 
 [testenv:docs]
+description =
+  Build main documentation.
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
@@ -96,6 +98,8 @@ commands =
     sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:pdf-docs]
+description =
+  Build PDF documentation.
 envdir = {toxworkdir}/docs
 deps = {[testenv:docs]deps}
 commands =
@@ -104,6 +108,9 @@ commands =
   make -C doc/build/pdf
 
 [testenv:releasenotes]
+description =
+  Generate release notes.
+envdir = {toxworkdir}/docs
 deps = {[testenv:docs]deps}
 commands = sphinx-build -a -W -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
@@ -111,9 +118,12 @@ commands = sphinx-build -a -W -E -d releasenotes/build/doctrees -b html releasen
 commands = oslo_debug_helper -t cyborg/tests {posargs}
 
 [testenv:api-ref]
+description =
+  Generate the API ref. Called from CI scripts to test and publish to docs.openstack.org.
 # This environment is called from CI scripts to test and publish
 # the API Ref to docs.openstack.org.
-deps = -r{toxinidir}/doc/requirements.txt
+envdir = {toxworkdir}/docs
+deps = {[testenv:docs]deps}
 commands =
   rm -rf api-ref/build
   sphinx-build -W -b html -d api-ref/build/doctrees api-ref/source api-ref/build/html