Enable multiplexing for SSH fixtures

To lesson load on gitlab.cern.ch and also github.com use SSH multiplexing for the fixtures.

Created a test image and

podman run  -it gitlab-registry.cern.ch/ai/it-puppet-module-ci_images:alma9-puppet-ci-2.8.1-rc0  /bin/bash

# cat ~/.ssh/config 
Host *
        StrictHostKeyChecking no
        ControlMaster auto
        ControlPath ~/.ssh/ssh-%r@%h:%p
        ControlPersist yes

And testing with a torture fixtures https://gitlab.cern.ch/ai/it-puppet-hostgroup-box/-/blob/qa/code/.fixtures.yml?ref_type=heads

running

 time BUNDLE_GEMFILE=../ci/Gemfile bundle exec rake --rakefile ../ci/Rakefile spec_prep

without multiplexing.

real    0m10.538s
user    0m2.410s
sys     0m1.875s

and with multiplexing

real    0m4.546s
user    0m1.784s
sys     0m1.756s