Fix hash-bang directive in nova_create_flavors.sh

The script employs bash-isms, so the directive to use the
Bourne shell causes some predictable failures:

  nova_create_flavors.sh: [[: not found

... etc.

Change-Id: I60f3de55d2ebbfa47d444ec72c07728bbfa38be6

tools/nova_create_flavors.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 # Create additional nova instance types (flavors)
 # to map to the AWS instance types we have in the templates