Fix ActiveSupport::Testing::Isolation on jruby

Hopefully the first of many related to #11700.

With these changes the railties tests wont 100% pass but at least they
will run and show the errors.

The first problem was the @method_name variable was never set.
This was causing ENV["ISOLATION_TEST"] to always be nil which
would cause the test output to never be written to the tempfile.

The second problem was that an invalid -t option was being passed
to minitest and minitest was erroring out.

The third problem was the run method needs to always return an
instance of the test class it is trying to isolate. We were returning
a ProxyTestResult instead.
Add timeout to test_async_stream

Without timeout:
this test executed infinitely on JRuby
Passes on MRI

With Timeout:
this test gracefully fails on JRuby
Passes on MRI, tested on v2.0 & v1.9.3
Merge pull request #11712 from atambo/activesupport_testing_isolation_jruby

Fix ActiveSupport::Testing::Isolation on jruby
Fix jruby warning when capture calls unlink on an open tempfile

Jruby cannot unlink a tempfile unless it is closed first.
Merge pull request #11725 from atambo/jruby_capture_unlink

Fix jruby warning when capture calls unlink on an open tempfile
Merge pull request #11721 from gaurish/join-timeout

Add timeout to test_async_stream
add a test for concat on hm:t associations
Isolate railties Generators Tests

With this change jruby should pass all of the railties tests.
Merge pull request #11726 from atambo/isolate_generator_tests

Isolate railties Generators Tests
Revert "Isolate railties Generators Tests"

This fixes railties tests in JRuby but break it in MRI
This reverts commit fea99276c7024f183bf72a16ad9f36af4bae1d42.