Micro-optimization: replace s.find(x)!=-1 with x in s

timeit shows a speedup of ~3x on Python 2.7.5 x86_64.
It also makes the code a bit shorter.

library/commands/command

@@ -180,7 +180,7 @@ class CommandModule(AnsibleModule):
         params['removes'] = None
         params['shell'] = False
         params['executable'] = None
-        if args.find("#USE_SHELL") != -1:
+        if "#USE_SHELL" in args:
             args = args.replace("#USE_SHELL", "")
             params['shell'] = True