Persist password (#393)

* never hold the owner of the room on the waiting screen

* persist room passwords so we can always call create meeting, even if it's already running, to avoid any inconsistency or race condition when joining a meeting

* Fixed issues in migration, room attribute updates, random_password and tests

db/migrate/20190312003555_add_password_to_rooms.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class AddPasswordToRooms < ActiveRecord::Migration[5.0]
+  def change
+    add_column :rooms, :moderator_pw, :string
+    add_column :rooms, :attendee_pw, :string
+    Room.reset_column_information
+    Room.all.each do |room|
+      room.update_attributes!(
+        moderator_pw: RandomPassword.generate(length: 12),
+        attendee_pw: RandomPassword.generate(length: 12)
+      )
+    end
+  end
+end