tox: Stop building *all* docs in 'docs'

The 'docs' target currently builds the documentation trees in 'api-ref' and
'api-guide', in addition to 'doc'. This massively increases the amount of
time docs take to build both locally and in the gate. It's not necessary for
gate, since separate jobs take care of the other documents for barbican.
As such, we should stop doing it.

For users that *do* care about this (for whatever reason) a new 'all-docs'
target is included.

Change-Id: I8b65c16d7bf574f045b702de853ad81389f140d5

tox.ini

@@ -76,13 +76,14 @@ commands =
   flake8 barbican setup.py
 
 [testenv:docs]
+# This environment is called from CI scripts to test and publish
+# the main docs to https://docs.openstack.org/barbican
+description = Build main documentation
 basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands=
-    rm -rf doc/build api-guide/build api-ref/build
+    rm -rf doc/build
     sphinx-build -W -b html doc/source doc/build/html
-    sphinx-build -W -b html api-guide/source api-guide/build/html
-    sphinx-build -W -b html api-ref/source api-ref/build/html
 whitelist_externals = rm
 
 [testenv:api-guide]
@@ -101,6 +102,17 @@ commands =
   rm -rf api-ref/build
   sphinx-build -W -b html -d api-ref/build/doctrees api-ref/source api-ref/build/html
 
+[testenv:all-docs]
+description = Build all documentation
+basepython = python3
+deps = -r{toxinidir}/doc/requirements.txt
+commands=
+    {[testenv:docs]commands}
+    {[testenv:api-guide]commands}
+    {[testenv:api-ref]commands}
+    {[testenv:releasenotes]commands}
+whitelist_externals = rm
+
 [testenv:functional]
 # This tox env is purely to make local test development easier
 # Note: This requires local running instances of Barbican and Keystone