Don't assume cache_dir is set in conf during uninstall
    
    The code was unconditionally retrieving a value from
    ipsilon.conf and replacing strings in it. This would fail
    if the config file didn't exist, there was no global section
    or if cache_dir wasn't there.
    
    https://fedorahosted.org/ipsilon/ticket/186
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>