unlink UNIXSocket files, fix Binder#close

[MSP-Greg]

See PR #1886, etc. Tests to follow after lib file PR's.

[MSP-Greg]

I think a 'perfect storm' happened on Travis, in that every intermittent test failed...

[nateberkopec]

AFAICT in your PRs theres still no test anywhere that paths are removed after stop, is that correct? We need that test.

[MSP-Greg]

I've got an update for PR #1965 that I just pushed...

puma/test/helpers/integration.rb

Lines 21 to 38 in fe6ddcd

	def teardown
	if defined?(@server) && @server
	stop_server @pid, signal: :INT
	end
	@ios_to_close.each do |io|
	io.close if io.is_a?(IO) && !io.closed?
	io = nil
	end
	refute File.exist?(@bind_path), "Bind path must be removed after stop"
	File.unlink(@bind_path) rescue nil
	# wait until the end for OS buffering?
	if defined?(@server) && @server
	@server.close unless @server.closed?
	@server = nil
	end
	end

[nateberkopec]

Merging with the understanding that tests are in the other PR.

Closes #1842 #1842 (comment)

[rromanchuk]

Why did i open my mouth... ugghh. On second deploy lol

Sep 19 22:05:19 web_worker2-0cd ansible-systemd[12153]: Invoked with no_block=False force=None name=puma.service enabled=None daemon_reload=False state=restarted masked=None scope=None user=None
Sep 19 22:05:19 web_worker2-0cd systemd[1]: Stopping Puma HTTP Server...
-- Subject: Unit puma.service has begun shutting down
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Unit puma.service has begun shutting down.
Sep 19 22:05:19 web_worker2-0cd puma[31897]: [31897] - Gracefully shutting down workers...
Sep 19 22:05:19 web_worker2-0cd puma[31897]: On worker shutdown...
Sep 19 22:05:19 web_worker2-0cd puma[31897]: On worker shutdown...
Sep 19 22:05:19 web_worker2-0cd puma[31897]: On worker shutdown...
Sep 19 22:05:19 web_worker2-0cd nginx[5011]: web_worker2-0cd nginx:  - - [19/Sep/2019:22:05:19 +0000] "GET /cable HTTP/1.1" 101 13306 "-" "-"
Sep 19 22:05:19 web_worker2-0cd systemd[1]: Stopped Puma HTTP Server.
-- Subject: Unit puma.service has finished shutting down
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Unit puma.service has finished shutting down.
Sep 19 22:05:19 web_worker2-0cd systemd[1]: Started Puma HTTP Server.
-- Subject: Unit puma.service has finished start-up
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Unit puma.service has finished starting up.
-- 
-- The start-up result is RESULT.
Sep 19 22:05:19 web_worker2-0cd sudo[12151]: pam_unix(sudo:session): session closed for user root
Sep 19 22:05:20 web_worker2-0cd puma[12159]: % Registered unix:/var/www/spar/shared/tmp/sockets/puma.sock for activation from LISTEN_FDS
Sep 19 22:05:20 web_worker2-0cd puma[12159]: [12159] Puma starting in cluster mode...
Sep 19 22:05:20 web_worker2-0cd puma[12159]: [12159] * Version 4.1.1 (ruby 2.6.3-p62), codename: Fourth and One
Sep 19 22:05:20 web_worker2-0cd puma[12159]: [12159] * Min threads: 10, max threads: 10
Sep 19 22:05:20 web_worker2-0cd puma[12159]: [12159] * Environment: production
Sep 19 22:05:20 web_worker2-0cd puma[12159]: [12159] * Process workers: 3
Sep 19 22:05:20 web_worker2-0cd puma[12159]: [12159] * Preloading application
Sep 19 22:05:20 web_worker2-0cd sudo[12226]:   ubuntu : TTY=pts/0 ; PWD=/home/ubuntu ; USER=root ; COMMAND=/bin/sh -c echo BECOME-SUCCESS-wurzdukaruyetpdclhiqhmcqfsrgyxgj; TMP=/home/ubuntu/tmp TMPDIR=/home/ubuntu/tmp RAILS_ENV=production /usr/bin/python /home/ubuntu/.ansible/tmp/ansible-tmp-1568930720.59-270557708308645/AnsiballZ_systemd.py
Sep 19 22:05:20 web_worker2-0cd sudo[12226]: pam_unix(sudo:session): session opened for user root by ubuntu(uid=0)
Sep 19 22:05:20 web_worker2-0cd ansible-systemd[12228]: Invoked with no_block=False force=None name=nginx enabled=None daemon_reload=False state=started masked=None scope=None user=None
Sep 19 22:05:20 web_worker2-0cd sudo[12226]: pam_unix(sudo:session): session closed for user root
Sep 19 22:05:21 web_worker2-0cd nginx[5011]: web_worker2-0cd nginx: 2019/09/19 22:05:21 [crit] 5011#5011: *991790 connect() to unix:///var/www/spar/shared/tmp/sockets/puma.sock failed (2: No such file or directory) while connecting to upstream, client: , server: , request: "GET /status HTTP/1.1", upstream: "http://unix:///var/www/spar/shared/tmp/sockets/puma.sock:/status", host: