add a disable_version_manifest accessor (#220)

* add a disable_version_manifest accessor

* allow version manifests to be disabled

* remove an extra blank line to keep rubocop happy

* fix syntax

lib/omnibus/project.rb

@@ -1443,8 +1443,10 @@ def build
       # Install shipped sources in the sources/ folder
       install_sources
 
-      write_json_manifest
-      write_text_manifest
+      unless @disable_version_manifest
+        write_json_manifest
+        write_text_manifest
+      end
       unless @skip_healthcheck
         HealthCheck.run!(self)
       end
@@ -1626,6 +1628,16 @@ def skip_healthcheck(val)
       end
     end
     expose :skip_healthcheck
+
+    def disable_version_manifest(val)
+      if val.nil?
+        @disable_version_manifest
+      else
+        @disable_version_manifest = val
+      end
+    end
+    expose :disable_version_manifest
+
     #
     # @!endgroup
     # --------------------------------------------------