Drop Python 2.6 support, update tox environments
    
    RHEL 6 doesn't go EOL till November, but the tests mysteriously
    fail on EPEL 6 since 4.3.0, tox in current Fedoras can't run a
    py26 environment any more, and my quotient of f**s to give is
    running low...so we officially don't support py26 any more as of
    now. Next on the chopping block: py27.
    
    This drops py26 (and all the special handling for it) from the
    tox configuration, and updates some code to use syntax that only
    works in 2.7 or later, and drops various annoying workarounds
    that were only needed for RHEL 6 / Python 2.6 compatibility in
    other ways.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>