test/drb/test_drb.rb: Specify the host of DRbServer

	to try fixing the following error.

	http://rubyci.s3.amazonaws.com/opensuseleap/ruby-master/log/20210407T063004Z.log.html.gz
	```
	[  605/21105] DRbTests::TestDRbSSLAry#test_06_next/home/chkbuild/chkbuild/tmp/build/20210407T063004Z/ruby/lib/drb/drb.rb:1138:in `method_missing': undefined method `regist' for [1, 2, "III", 4, "five", 6]:Array (NoMethodError)
		from /home/chkbuild/chkbuild/tmp/build/20210407T063004Z/ruby/lib/drb/extserv.rb:21:in `block in initialize'
		from /home/chkbuild/chkbuild/tmp/build/20210407T063004Z/ruby/.ext/common/monitor.rb:202:in `synchronize'
		from /home/chkbuild/chkbuild/tmp/build/20210407T063004Z/ruby/.ext/common/monitor.rb:202:in `mon_synchronize'
		from /home/chkbuild/chkbuild/tmp/build/20210407T063004Z/ruby/lib/drb/extserv.rb:20:in `initialize'
		from /home/chkbuild/chkbuild/tmp/build/20210407T063004Z/ruby/test/drb/ut_array_drbssl.rb:35:in `new'
		from /home/chkbuild/chkbuild/tmp/build/20210407T063004Z/ruby/test/drb/ut_array_drbssl.rb:35:in `<main>'
	 = 100.05 s
	```

	Here is my analysis:
	The test of drb used both `druby://:0` and `druby://localhost:0` for
	DRbServer. However, the former listens on IPv4, and the latter does on
	IPv6, depending on environments. The port 0 is automatically assigned,
	but sometimes the same port is used to both because they are different
	protocols (IPv4 and IPv6). In this case, their URIs are resolved to the
	completely same one (`druby://localhost:port`), which confuses the
	method `DRb.here?` which determines the DRbObject is remote or local.

	This changeset uses `druby://localhost:0` consistently.
	---
	 test/drb/test_drb.rb    | 4 ++--
	 test/drb/test_drbssl.rb | 2 +-
	 2 files changed, 3 insertions(+), 3 deletions(-)

[Bug #16634]

(cherry picked from commit fb472ca7adbaceb35aae1b3a6b948720ffc9eb53)

and add more stop_pool after stop_service

This reverts commit f289e3994bbc6560e2e4e5905b52c35c829c972d.

This removes the related tests, and puts the related specs behind
version guards.  This affects all code in lib, including some
libraries that may want to support older versions of Ruby.

My previous fix in d0ed935d5bf8c3fce9800742a36e44fb7f63dda4 was
not correct, as pointed out by cremno on GitHub.

This simplifies things by just using Kernel#to_s.  Also switch to
bind_call(obj) instead of bind(obj).call for better performance.

This rescues some exceptions that could happen with a closed or
shutdown DRb socket. This can prevent the server from
exiting if an client socket is closed directly after it is
accepted.

Fixes [Bug #8039]

* Handle BasicObject in drb

Also fix a bug in rescue clause of any_to_s because sprintf
does not handle the %l modifier.

Fixes [Bug #7833]

* Do not send a reply to the client if there is a connection error

This allows for normal TCP shutdown (fin-ack-fin-ack instead of
fin-ack-push-rst).

Patch from pierre@mouraf.org (Pierre-Alexandre Meyer).

Fixes [Bug #2339]

* Detect fork and do not reuse forked connections in drb

This associates each DRbConn with a pid, and if the pid changes,
it closes any DRbConns in the pool with a pid that no longer
matches.  This fixes DRb servers from sending messages intended
for one client to another client after forking.

Fixes [Bug #2718]
Fixes [Bug #14471]

The test seems to have a race condition, which fails on very slow
machine like Solaris10s.  So skip it.

In addition, this change restores timeout guard that was removed at
0660d7cb538cf5284d50f66adfcbd78609839715.  This is because the test gets
stuck forever when something wrong occurs.  It is better to fail the
test than stuck.