test-case: Clean up jackd before latency test

Sometimes when timeout is reached, the latency test does not terminate
the jackd process. This commit adds `pkill jackd` on test setup to
ensure no instance od `jackd` is running.

Signed-off-by: Pawel Langowski <pawelx.langowski@intel.com>

Author: PLangowski

test-case/latency-metrics.sh

@@ -260,6 +260,7 @@ report_end()
 
 main()
 {
+  pkill jackd || True
   check_latency_options
 
   setup_kernel_check_point