[3.12] gh-100985: Consistently wrap IPv6 IP address during CONNECT (GH-100986) (GH-115591)

Update _get_hostport to always remove square brackets
from IPv6 addresses. Then add them if needed
in "CONNECT .." and "Host: ".
(cherry picked from commit 465db27cb983084e718a1fd9519b2726c96935cb)

Co-authored-by: Derek Higgins <derekh@redhat.com>