Replace print statements with six.print_() calls

Using the print statement as though it was a function leads to
incorrect behaviour in a python2 runtime. E.g.:

        print()
        print( "Some examples:")
        print()

Produces:

        ()
        Some examples:
        ()

Instead replace use of the print keyword with a call to the six
module's print_() function.

Fixes Issue #219

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>