make compile_assets work when there’s no db.yml

Fixes: CNVS-39854

Test plan:
* mv config/database.yml config/database.yml.backup
* bundle exec rake canvas:compile_assets
* it should work
* Docker build should pass

Change-Id: I0786d1de1d6f6f69d665e10b0428571e77d7f859
Reviewed-on: https://gerrit.instructure.com/128974
Reviewed-by: James Williams  <jamesw@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>

config/initializers/revved_asset_urls.rb

@@ -19,7 +19,11 @@
 # instead of doing it's normal cache busting stuff on the url.
 # eg: instead of '/images/whatever.png?12345', we want '/dist/images/whatever-<md5 of file>.png'.
 # There is a different method that needs to be monkeypatched for rails 3 vs rails 4
-require 'action_view/helpers/asset_url_helper'
+
+
+
+require 'action_view/helpers'
+
 module RevAssetPaths
   def path_to_asset(source, options = {})
     original_path = super

lib/tasks/css.rake

@@ -9,6 +9,7 @@ namespace :css do
   task :compile do
     # try to get a conection to the database so we can do the brand_configs:write below
     require 'config/environment' rescue nil
+    require 'config/initializers/revved_asset_urls'
     require 'lib/brandable_css'
     puts "--> Starting: 'css:compile'"
     time = Benchmark.realtime do