Properly initialize ccaches before storing into them
    
    krb5_cc_new_unique() doesn't initialize ccaches, which results in the
    krb5 libraries being aware of their presence within the collection but
    being unable to manipulate them.
    
    This is transparent to most gssproxy consumers because we just
    re-fetch the ccache on error.
    
    Signed-off-by: Robbie Harwood <rharwood@redhat.com>
    Reviewed-by: Simo Sorce <simo@redhat.com>
    Merges: #223