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
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