Update Apache + mod_wsgi deployment mechanisms

Added a global toggle for enabling HTTPD + mod_wsgi for services
that default deploy to running under Apache. When the variable
``ENABLE_HTTPD_MOD_WSGI_SERVICES`` is set to ``True`` any service
that recommends deploying under HTTPD + mod_wsgi, will be run
under Apache.

If ``ENABLE_HTTPD_MOD_WSGI_SERVICES`` is set to ``False`` the
any service that is defaulted to running under HTTPD + mod_wsgi
will (if capable) be run in an alternate deployment strategy (e.g.
eventlet).

Updated Swift and Keystone to have individual toggles for deploying
under HTTPD + mod_wsgi. This is done to allow for gate to run on
the services under mod_wsgi where appropriate. Toggles are
``KEYSTONE_USE_MOD_WSGI`` and ``SWIFT_USE_MOD_WSGI`` and are both
defaulted to "False" (do not deploy under HTTPD + mod_wsgi).

Change-Id: Id3b121b8f1cde369d184b586e0d875bdbda34813
diff --git a/README.md b/README.md
index 54535fe..7185e9d 100644
--- a/README.md
+++ b/README.md
@@ -133,11 +133,23 @@
 
 # Apache Frontend
 
-Apache web server is enabled for wsgi services by setting
-`APACHE_ENABLED_SERVICES` in your ``localrc`` section.  Remember to
-enable these services at first as above.
+Apache web server can be enabled for wsgi services that support being deployed
+under HTTPD + mod_wsgi. By default, services that recommend running under
+HTTPD + mod_wsgi are deployed under Apache. To use an alternative deployment
+strategy (e.g. eventlet) for services that support an alternative to HTTPD +
+mod_wsgi set ``ENABLE_HTTPD_MOD_WSGI_SERVICES`` to ``False`` in your
+``local.conf``.
 
-    APACHE_ENABLED_SERVICES+=key,swift
+Each service that can be run under HTTPD + mod_wsgi also has an override
+toggle available that can be set in your ``local.conf``.
+
+Example (Keystone):
+
+    KEYSTONE_USE_MOD_WSGI="True"
+
+Example (Swift):
+
+    SWIFT_USE_MOD_WSGI="True"
 
 # Swift