oft: Name constants in UPPERCASE

Signed-off-by: Stephen Finucane <stephenfinucane@hotmail.com>
oft: Convert to print_function

Replace the Python 'print' keyword ('print x') with the function
version ('print(x)'). This is the recommended approach for new Python
code.

In addition, replace a number of 'print' calls with either logging or
calls to 'die' to be consistent.

Signed-off-by: Stephen Finucane <stephenfinucane@hotmail.com>
Merge into master from pull request #142:
Python 2.7 Updates (https://github.com/floodlight/oftest/pull/142)