python path not always the same

On macos python3  default installation path is not /usr/bin. Adjusting launch path to allow for more accessibility
    
Signed-off-by: Chris Austen austenc@us.ibm.com
diff --git a/thalerj/openbmctool.py b/thalerj/openbmctool.py
index d61a35c..8a3043a 100644
--- a/thalerj/openbmctool.py
+++ b/thalerj/openbmctool.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 """
  Copyright 2017 IBM Corporation