[DOCS] Added release-name as a watermark to Docs.

Added a water mark to the role documentation
to make clear to deployers which release they're
working with.

Modified conf.py that adds watermark to the documentation according
to particular branch. If the current branch is master than
watermark is 'Pre-release' and if the current branch is
stable/<release-name> than watermark is <release-name>.

This is a combined implementation based on the following
patches:
- https://review.openstack.org/372565
- https://review.openstack.org/382637
- https://review.openstack.org/384140

Change-Id: Icc1c4f2c26df08aefcf6cc613232e650162e665e

doc/source/conf.py

@@ -22,6 +22,7 @@
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 
+import openstackdocstheme
 import pbr.version
 import os
 
@@ -131,7 +132,7 @@ todo_include_todos = False
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-# html_theme = 'alabaster'
+html_theme = 'openstackdocs'
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
@@ -139,7 +140,7 @@ todo_include_todos = False
 # html_theme_options = {}
 
 # Add any paths that contain custom themes here, relative to this directory.
-# html_theme_path = []
+html_theme_path = [openstackdocstheme.get_html_theme_path()]
 
 # The name for this set of Sphinx documents.  If None, it defaults to
 # "<project> v<release> documentation".
@@ -306,9 +307,11 @@ texinfo_documents = [
 # If true, do not generate a @detailmenu in the "Top" node's menu.
 # texinfo_no_detailmenu = False
 
-watermark = os.popen("git branch --contains $(git rev-parse HEAD) | awk -F/ '/stable/ {print $2}'").read().strip(' \n\t').capitalize()
+
+watermark = os.popen("git branch --contains $(git rev-parse HEAD)\
+| awk -F/ '/stable/ {print $2}'").read().strip(' \n\t').capitalize()
 if watermark == "":
-  watermark = "Pre-release"
+    watermark = "Pre-release"
 
 # -- Options for sphinxmark -----------------------------------------------
 sphinxmark_enable = True

test-requirements.txt

@@ -11,6 +11,7 @@ ndg-httpsclient>=0.4.2;python_version<'3.0' # BSD
 # this is required for the docs build jobs
 sphinx!=1.3b1,<1.4,>=1.2.1 # BSD
 oslosphinx>=4.7.0 # Apache-2.0
+openstackdocstheme>=1.5.0 # Apache-2.0
 doc8 # Apache-2.0
 reno>=1.8.0 # Apache2
 sphinxmark>=0.1.14 # Apache-2.0