fix: bin/emqx change use ps -p to check if pid is running

bin/emqx

@@ -302,9 +302,11 @@ bootstrapd() {
 # check if a PID is down
 is_down() {
     PID="$1"
-    if kill -s 0 "$PID" 2>/dev/null; then
+    if ps -p "$PID" >/dev/null; then
+        # still alive
         return 1
     fi
+    # it's gone
     return 0
 }
 
@@ -484,7 +486,8 @@ case "$1" in
             exit 1
         fi
         WAIT_TIME="${WAIT_FOR_ERLANG_STOP:-60}"
-        if ! wait_for "$WAIT_TIME" is_down "$PID"; then
+        if ! wait_for "$WAIT_TIME" 'is_down' "$PID"; then
+            ps -p "$PID"
             msg="dangling after ${WAIT_TIME} seconds"
             # also log to syslog
             logger -t "${REL_NAME}[${PID}]" "STOP: $msg"