Migrate the four pause tests to the Scenario DSL: the invariant is the
container state (paused/running), not an HTTP timeout, so the scenarios
observe state and drop the port-mapping helpers and the pause fixture.
ExitCode joins the check vocabulary for error-path steps, paired with
MayFail. TestPauseServiceDoesNotExist now locks the current behavior —
pause of an unknown service is rejected with 'no such service' — which
resolves the TODO the legacy test carried: it asserted exit 0 while
wishing for an error, and the CLI has since started validating selected
services.
Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>
