Removing buggy undocumented feature ...

... according to discussion at
https://github.com/jimis/core/commit/d4999f291bf937ef36ee05c28149ca773b172865
Fix selectservers().

See Redmine #5458. Thanks to Bob Ingersoll for spotting it.
Add acceptance test for selectservers().
TryConnect() should return error when select() times out.
Logging in milliseconds is ugly.
Fix socket descriptor leak.
Acceptance test for selectservers() now checks failures as well as successes.

Unfortunately some requests may timeout, which means that the test will
take 30s to complete. In the future we should enable parallel test
harness to avoid waiting.
Selectservers() now logs INFO in case of timeout.
Beautify message.
Use dcs_passif_expected() to check and report all classes are set.
Change timeout so that acceptance test takes only 5 seconds instead of 30.

Does not work for now, should work after redmine #5497 gets fixed.
Merge branch 'jimis/selectservers' into 3.6.x