Fix wrong option name in kolla-build.conf

The install type can now be change by specifying the correct option
name.

Change-Id: I612afc3df1e0e1bdfa9243417537eb176f0d89cc
Closes-Bug: #1501327

etc/kolla/kolla-build.conf

@@ -15,7 +15,7 @@
 #base_tag = latest
 
 # The method of the OpenStack install
-#type = binary
+#install_type = binary
 
 # Do not use Docker cache when building
 #no_cache = False