Run Tests against JRuby master

Many of the failing tests in rails test suite fail because of missing encoding support, example #11739


And according to recent announcement, lot of encoding issues have been fixed in current master.  http://ruby.11.x6.nabble.com/Big-encoding-patches-landed-on-master-td4993719.html


So lets test against JRuby master & incase there are still bugs. it would be easier to report them to JRuby.
Merge pull request #12294 from gaurish/patch-1

Run Tests against JRuby master
Allow failures in jruby-head
Merge pull request #12295 from gaurish/patch-2

Allow failures in jruby-head
Drying up method_missing code
Initializing Codepoint object with default values
mention controller test base class in testing guide. [ci skip]
Allow attaching to AS::Notifications namespace up front

Before, you were required to attach *after* adding the methods to the
class, since the attachment process needed the methods to be present.

With this change, any new method will also be attached to the configured
namespace.
Merge pull request #12299 from hitendrasingh/code_refactor

DRYing up method_missing code; Initializing Codepoint object with default values
Merge pull request #12285 from dasch/dasch/allow-attaching-up-front

Allow attaching to AS::Notifications namespace up front