util: changed shebang on gem5img.py to python2.7

Change-Id: Id1a2112ce940bf6721609e2637d925d35e5ded8a
Signed-off-by: Ryan Gambord <gambordr@oregonstate.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17408
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
diff --git a/util/gem5img.py b/util/gem5img.py
index f02ccb1..607f034 100755
--- a/util/gem5img.py
+++ b/util/gem5img.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python2.7
 #
 # gem5img.py
 # Script for managing a gem5 disk image.