Rename docs to doc to align with OpenStack standard

This patchset updates docs to doc to align with OpenStack
standard. Follow-up patchset will be needed to publish
documentation to OpenStack [0].

[0] https://docs.openstack.org/doc-contrib-guide/project-guides.html

Change-Id: I90e5f9129207901402e26ed9488ec6e065568fe1

tools/gate/playbooks/zuul-linter.yaml

@@ -15,6 +15,6 @@
 - hosts: primary
   tasks:
     - name: Execute a Whitespace Linter check
-      command: find . -not -path "*/\.*" -not -path "*/docs/build/*" -not -name "*.tgz"  -type f -exec egrep -l " +$" {} \;
+      command: find . -not -path "*/\.*" -not -path "*/doc/build/*" -not -name "*.tgz"  -type f -exec egrep -l " +$" {} \;
       register: result
       failed_when: result.stdout != ""

tox.ini

@@ -26,8 +26,8 @@ commands =
 whitelist_externals = tox
 
 [testenv:docs]
-deps = -r{toxinidir}/docs/requirements.txt
+deps = -r{toxinidir}/doc/requirements.txt
 commands =
     rm -rf doc/build
-    sphinx-build -b html docs/source docs/build -n -W -v
+    sphinx-build -b html doc/source doc/build -n -W -v
 whitelist_externals = rm