tests/micropython: Add test for micropython.stack_use() function.

tests/micropython/stack_use.py

@@ -0,0 +1,7 @@
+# tests stack_use function in micropython module
+import micropython
+
+if not hasattr(micropython, 'stack_use'):
+    print('SKIP')
+else:
+    print(type(micropython.stack_use())) # output varies

tests/micropython/stack_use.py.exp

@@ -0,0 +1 @@
+<class 'int'>