support/testing: make treq tests to ignore warning

support/testing: make treq tests to ignore warning

Newer versions of python-treq display a warning at runtime when
service_identity is not installed:
"Without the service_identity module, Twisted can perform only
rudimentary TLS client hostname verification."

This warning message confuses the test that looks for another string in
stdout. Make the test ignore other messages while still expecting
"Connection refused".

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/269139449
https://gitlab.com/buildroot.org/buildroot/-/jobs/269139450

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>