Add quotes for -n

According to SC2070, -n doesn't work with unquoted arguments
https://github.com/koalaman/shellcheck/wiki/SC2070

Signed-off-by: Gaoyi <ymuemc@163.com>

test/units/testsuite-36.sh

@@ -120,7 +120,7 @@ systemctlCheckNUMAProperties() {
 
     > "$LOGFILE"
 
-    if [ -n $3 ]; then
+    if [ -n "$3" ]; then
         systemctl show -p NUMAMask $1 > "$LOGFILE"
         grep "NUMAMask=$3" "$LOGFILE"
     fi