Remove the watcher sample configuration file

Watcher sample configuration file groups parameters from
various projects and the watcher project ones. This makes it
tricky to review updates on configuration parameters.

It is inconvenient for developer if the add/remove/change some
configuration options cause they need to take care about the
config.sample file.

The sample configuration file should be available into HTML doc.

This patchset:
. removes the file /etc/watcher/watcher.conf.sample
. adds an admin script tool to be able to built it, by using tox
. includes a new section 'Watcher sample configuration files' into
  the doc source files
. uses sphinx extension oslo_config.sphinxgenconfig

Change-Id: If2180de3614663f9cbc5396961a8d2175e28e315
Closes-Bug: #1541734

doc/source/conf.py

@@ -18,6 +18,7 @@ from watcher import version as watcher_version
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = [
+    'oslo_config.sphinxconfiggen',
     'sphinx.ext.autodoc',
     'sphinx.ext.viewcode',
     'sphinxcontrib.httpdomain',
@@ -28,7 +29,8 @@ extensions = [
 ]
 
 wsme_protocols = ['restjson']
-
+config_generator_config_file = '../../etc/watcher/watcher-config-generator.conf'
+sample_config_basename = 'watcher'
 
 # autodoc generation is a bit aggressive and a nuisance when doing heavy
 # text edit cycles.