zopewsgi: run waitress with asyncore_use_poll by default

on python2, we use have a [python patch][patch] to globally make
asyncore use poll, at that time we were using medusa and it was not
exposing an option to use something else than select.

[patch]: https://lab.nexedi.com/nexedi/slapos/-/blob/180f1553fa7774f05ae8e739dfef43fa2ae56c0a/component/python-2.7/asyncore_poll_insteadof_select.patch
9 jobs for for_testrunner_1 in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

01:15:04

passed ERP5.CodingStyleTest-TestRunner1

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failed ERP5.PerformanceTest-Master

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failed ERP5.PerformanceTest-TestRunner1

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failed ERP5.UnitTest-Master

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passed ERP5.UnitTest-TestRunner1

01:31:18

passed SlapOS.Eggs.UnitTest-Master.Python2

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passed SlapOS.Eggs.UnitTest-Master.Python3

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passed Wendelin.UnitTest-Master

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