test/system: do not run "podman pause/unpause" in parallel

podman ps -a causes unexpected timing delays as it tries to take locks for
all containers and parallel tests may cause it to block for a while.

In CI logs I see ps -a take over 3 seconds which is enough to mess with
the expect time and make the test fail. Since testing the ps -a output
as part of the test just switch the test to not run in parallel.

This failed with "delta t between paused and restarted" where it took 10
seconds instead of the max expected 6 seconds.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>