[1.5.x] Fixed #19172 -- Isolated poisoned_http_host tests from 500 handlers
[1.5.x] Fixed #19172 -- Isolated poisoned_http_host tests from 500 handlers

Thanks bernardofontes for the report.

Backport of b774c5993 from master.

ccn-2m/django,bliti/django-nonrel-1.5,ccn-2m/django,imtapps/django-imt-fork,imtapps/django-imt-fork,alx-eu/django,alx-eu/django,hasadna/django,alx-eu/django,alx-eu/django,bliti/django-nonrel-1.5,hasadna/django,bliti/django-nonrel-1.5,ccn-2m/django,hasadna/django,imtapps/django-imt-fork,ccn-2m/django