Allow dynamic accessory files to reference declared ENVs

test/configuration/accessory_test.rb

@@ -98,7 +98,8 @@ class ConfigurationAccessoryTest < ActiveSupport::TestCase
     @deploy[:accessories]["mysql"]["files"] << "test/fixtures/files/structure.sql.erb:/docker-entrypoint-initdb.d/structure.sql"
     @config = Mrsk::Configuration.new(@deploy)
 
-    assert_equal "This was dynamically expanded", @config.accessory(:mysql).files.keys[2].read
+    assert_match "This was dynamically expanded", @config.accessory(:mysql).files.keys[2].read
+    assert_match "%", @config.accessory(:mysql).files.keys[2].read
   end
 
   test "directories" do

test/fixtures/files/structure.sql.erb

@@ -1 +1,2 @@
-<%= "This was dynamically expanded" %>
+<%= "This was dynamically expanded" %>
+<%= ENV["MYSQL_ROOT_HOST"] %>