perf test lock_contention.sh: Skip test if not enough CPUs

Machines with less then 4 CPUs weren't consistently triggering lock
events required for the test.

Skip the test on those machines. The limit of 4 CPUs is set as it
generates around 100 lock events for a test.
Signed-off-by: Veronika Molnarova <vmolnaro@redhat.com>
Acked-by: Michael Petlan <mpetlan@redhat.com>
Link: https://lore.kernel.org/r/20230919150419.23193-2-vmolnaro@redhat.comSigned-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/tests/shell/lock_contention.sh

@@ -32,6 +32,12 @@ check() {
 		err=2
 		exit
 	fi
+
+	if [ `nproc` -lt 4 ]; then
+		echo "[Skip] Low number of CPUs (`nproc`), lock event cannot be triggered certainly"
+		err=2
+		exit
+	fi
 }
 
 test_record()