Fix test_proc_kill hanging

Sometimes the signal is delivered to memcg_process before the framework took
into consideration its pid entered in the tasks. Fixed by delaying the signal
send command.

Signed-off-by: George Nita <george.nita@enea.com>
Upstream-Status: Pending 

diff --git a/testcases/kernel/controllers/memcg/functional/memcg_lib.sh b/testcases/kernel/controllers/memcg/functional/memcg_lib.sh
index ffbe006..e81bf74 100755
--- a/testcases/kernel/controllers/memcg/functional/memcg_lib.sh
+++ b/testcases/kernel/controllers/memcg/functional/memcg_lib.sh
@@ -220,8 +220,8 @@ test_proc_kill()
 
 	$TEST_PATH/memcg_process $2 -s $3 &
 	pid=$!
-	sleep 1
 	echo $pid > tasks
+	sleep 1
 
 	kill -s USR1 $pid 2> /dev/null
 	sleep 1