* Update test_integration files per PR #1956
test_integration_cluster.rb
Request handling during server TERM - two tests
`#test_term_closes_listeners_tcp`
`#test_term_closes_listeners_unix`
using `#term_closes_listeners`
Send requests 10 per second. Send 10, then :TERM server, then send another 30.
No more than 10 should throw Errno::ECONNRESET.
Request handling during phased restart - two tests
`#test_usr1_all_respond_tcp`
`#test_usr1_all_respond_unix`
using `#usr1_all_respond`
Send requests 1 per second. Send 1, then :USR1 server, then send another 24.
All should be responded to, and at least three workers should be used
Stuck worker tests - two tests
`#test_stuck_external_term_spawn`
Tests whether externally TERM'd 'stuck' workers are proper re-spawned.
`#test_stuck_phased_restart`
Tests whether 'stuck' workers are properly shutdown during phased-restart.
helper files/methods changes
1. helper file changes to allow binding to TCP or UNIX, see kwarg unix:
2. Skip on Windows for signal TERM
* Misc updates, debug output, cleanup
* Add comments
* fix test_int_signal_with_background_thread_in_jruby per review
* TestIntegrationCluster#term_closes_listeners - add interleaved assert
* cluster.rb - remove duplicate Worker#term? method
