Correct and make less confusing the conditional Python macros
    
    This was using 'python_sitelib' in a non-standard way (it got
    defined to either python2_sitelib or python3_sitelib depending
    on whether we're doing a python2 or python3 build). Igor saw
    the uses of 'python_sitelib' and assumed it was just using the
    old name for 'the python 2 sitelib' and changed them all to
    'python2_sitelib'...which broke all Fedora builds.
    
    This fixes that problem and renames the package's confusing
    'python_sitelib' and 'pythonbin' so hopefully no-one will make
    the same mistake in future.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>