Migrate twilio to use rails creds

fixes FOO-1496

Change-Id: I26e329e09022aecca3f575667fe5ff8c377eb24d
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/276546
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: Jacob Burroughs <jburroughs@instructure.com>
Product-Review: Jacob Burroughs <jburroughs@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>

lib/canvas/twilio.rb

@@ -23,16 +23,12 @@ require 'twilio-ruby'
 module Canvas::Twilio
   DEFAULT_COUNTRY = 'US'
 
-  def self.config
-    @config ||= ConfigFile.load('twilio') || {}
-  end
-
   def self.account_sid
-    config['account_sid']
+    Rails.application.credentials.twilio_creds&.[](:account_sid)
   end
 
   def self.auth_token
-    config['auth_token']
+    Rails.application.credentials.twilio_creds&.[](:auth_token)
   end
 
   def self.client

spec/lib/canvas/twilio_spec.rb

@@ -104,8 +104,8 @@ describe 'Canvas::Twilio' do
       )
     end
 
-    it 'raises an exception when attempting to deliver without a config file' do
-      allow(Canvas::Twilio).to receive(:config).and_return({})
+    it 'raises an exception when attempting to deliver without config' do
+      allow(Rails.application.credentials).to receive(:twilio_creds).and_return(nil)
 
       expect { Canvas::Twilio.deliver('+18015550100', 'message text') }.to raise_error("Twilio is not configured")
     end