Update plugin for and document per host overrides

Ensure that configuration section and key names are strings, as
required by RawConfigParser.write.
Document an example of overriding openstack configurations on a per host
basis.

Closes-Bug: #1536957
Change-Id: I6b641715766eb11910fcf7479e260f0e16cc1657

doc/source/install-guide/configure-openstack.rst

@@ -57,6 +57,25 @@ entry in ``/etc/openstack_deploy/user_variables.yml``:
         idle_timeout: 300
         max_pool_size: 10
 
+Overrides may also be applied on a per host basis with the following
+configuration in ``/etc/openstack_deploy/openstack_user_config.yml``:
+
+.. code-block:: yaml
+
+      compute_hosts:
+        900089-compute001:
+          ip: 192.0.2.10
+          host_vars:
+            nova_nova_conf_overrides:
+              DEFAULT:
+                remove_unused_original_minimum_age_seconds: 43200
+              libvirt:
+                cpu_mode: host-model
+                disk_cachemodes: file=directsync,block=none
+              database:
+                idle_timeout: 300
+                max_pool_size: 10
+
 This method may be used for any INI file format for all OpenStack projects
 deployed in OpenStack-Ansible.
 

playbooks/plugins/actions/config_template.py

@@ -67,17 +67,17 @@ class ActionModule(object):
             # If the items value is not a dictionary it is assumed that the
             #  value is a default item for this config type.
             if not isinstance(items, dict):
-                config.set('DEFAULT', section, str(items))
+                config.set('DEFAULT', str(section), str(items))
             else:
                 # Attempt to add a section to the config file passing if
                 #  an error is raised that is related to the section
                 #  already existing.
                 try:
-                    config.add_section(section)
+                    config.add_section(str(section))
                 except (ConfigParser.DuplicateSectionError, ValueError):
                     pass
                 for key, value in items.items():
-                    config.set(section, key, str(value))
+                    config.set(str(section), str(key), str(value))
         else:
             config_object.close()