Add toggle to run Heat API services via Apache2

Add templates for running Heat API services via
apache mod_wsgi. Also add appropriate functions to
lib/heat for configuring Heat.

Change-Id: I1bdd678c44ddfa616a9db7db85ff6f490ff08947
diff --git a/doc/source/configuration.rst b/doc/source/configuration.rst
index aae4f33..d70d3da 100644
--- a/doc/source/configuration.rst
+++ b/doc/source/configuration.rst
@@ -297,6 +297,12 @@
 
     SWIFT_USE_MOD_WSGI="True"
 
+Example (Heat):
+
+::
+
+    HEAT_USE_MOD_WSGI="True"
+
 
 Example (Cinder):