Change tests to always exercise ccache sycns
    
    Do not use a gssproxy side ccache in tests; instead, let them use the new
    default temporary memcache for operations.  Additionally, allow the proxy to
    always sync back ccaches on operations so that the sync path is exercised as
    well.
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    [rharwood@redhat.com: tweak commit message body]
    Reviewed-by: Robbie Harwood <rharwood@redhat.com>
    Merges: #162