Add LimitRequestBody to sample httpd config

Web servers that are exposed to the Internet eventually gain a
security feature of limiting the amount of data in the request
body. In Apache Httpd, this is provided by the LimitRequestBody
directive. This is added to the sample Httpd config file.

The limit is set for only the keystone services so it won't
affect other services running in Httpd.

The value of 114688 was picked because it's the current limit
on request body that oslo.middleware's sizelimit function puts
on requests to keystone.

Use of oslo.middleware's sizelimit re-implementation can be
deprecated.

Docs:
- http://httpd.apache.org/docs/2.4/mod/core.html#limitrequestbody

ReleaseNotesImpact

Closes-Bug: 1481048
Change-Id: I5509e4b65900c15dd0b5fda43b1d5bb4dc3ff5ff

httpd/wsgi-keystone.conf

@@ -7,6 +7,7 @@ Listen 35357
     WSGIScriptAlias / /usr/local/bin/keystone-wsgi-public
     WSGIApplicationGroup %{GLOBAL}
     WSGIPassAuthorization On
+    LimitRequestBody 114688
     <IfVersion >= 2.4>
       ErrorLogFormat "%{cu}t %M"
     </IfVersion>
@@ -30,6 +31,7 @@ Listen 35357
     WSGIScriptAlias / /usr/local/bin/keystone-wsgi-admin
     WSGIApplicationGroup %{GLOBAL}
     WSGIPassAuthorization On
+    LimitRequestBody 114688
     <IfVersion >= 2.4>
       ErrorLogFormat "%{cu}t %M"
     </IfVersion>