Return status from running command

This way when someone use code like `sys.exit(main())` it will have
proper exit code on error (so different than `0`).

Story: 2001246
Task: 5776

Change-Id: I1c04fbf73d1fc44da7738c8f22296992d2e7a4f8

monascaclient/shell.py

@@ -106,7 +106,7 @@ def main(args=None):
                 encoding = locale.getpreferredencoding()
                 if encoding:
                     args = map(lambda arg: arg.decode(encoding), args)
-        MonascaShell().run(args)
+        return MonascaShell().run(args)
     except Exception as e:
         if '--debug' in args or '-d' in args:
             raise