Add low memory device version of sched scenario group

replaced hackbench01 with hackbench01_low_mem in sched_low_mem

Original hackbench01 test case will run out of memory in android devices with low memory.
This script is created as a light version to the orignal sched test group for low memory devices.
On VTS scheduling, low memory device is determined through checking for system property 'ro.config.low_ram' and VTS will automatically use this script instead of original sched script if the property is set to be 'True' or 'true'

Bug: 63694670
Test: run vts-kernel
Change-Id: Ia5341765b9ac39bccaa8a7045eb543d7b361a8c5
(cherry picked from commit 47e8e7ba692ef873342cb9734e5b19b5dc74482d)
diff --git a/runtest/sched_low_mem b/runtest/sched_low_mem
new file mode 100644
index 0000000..48c1668
--- /dev/null
+++ b/runtest/sched_low_mem
@@ -0,0 +1,18 @@
+#DESCRIPTION: Scheduler Stress Tests for low memory android devices
+pth_str01 pth_str01
+pth_str02 pth_str02 -n1000
+pth_str03 pth_str03
+
+time-schedule01		time-schedule
+trace_sched01		trace_sched -c 1
+
+hackbench01_low_mem hackbench 15 process 1000
+hackbench02 hackbench 20 thread 1000
+
+sched_setattr01 sched_setattr01
+sched_getattr01 sched_getattr01
+sched_getattr02 sched_getattr02
+
+sched_cli_serv run_sched_cliserv.sh
+# Run this stress test for 2 minutes
+sched_stress sched_stress.sh