tests: switch to using key/value extra-vars instead of json

tests: switch to using key/value extra-vars instead of json

I continue to have issues with extra-vars as json. The latest issue
being that the ceph_docker_image_tag config option included in the json
was being ignored. I can't find the root cause, by using the key/value
format seems to work.

I've also removed several options here to simply the interface. We can
add those back if they become necessary.

Signed-off-by: Andrew Schoen <aschoen@redhat.com>
(cherry picked from commit e384b2498755e5537595158ca498e03013e33673)