Porting back STORM-1605: storm shell script should use /bin/env python to check python version

[Jungtaek Lim]

Hi devs,

Don't we want to port back STORM-1605 to 1.x version lines as well?
https://issues.apache.org/jira/browse/STORM-1605

Porting back doesn't require +1 (and doesn't even require PR), so I just
would want to double check with others before going forward.

Thanks,
Jungtaek Lim (HeartSaVioR)