Add support to force the RTEMS version. This remove the need for using
the --rtems-version command line option if the automatic detection fails.
Update all python code to support python 2 and 3.
Update rtems_waf to the latest version to support the RTEMS version,
check environment variables and to display the CC version.
Sort all tests. I think the unsorted list is dependent on the version
of python and so would result in repo noise as if it regenerted.
