commands: add python 2 pyi file (#698)

Partially fixes issue #531

stdlib/2/commands.pyi

@@ -0,0 +1,5 @@
+from typing import Tuple
+
+def getstatus(file: str) -> str: ...
+def getoutput(cmd: str) -> str: ...
+def getstatusoutput(cmd: str) -> Tuple[int, str]: ...