Clear kernel keyring in client installer, save dbdir on new connections
    
    This patch addresses two issues:
    
    1. If a client is previously enrolled in an IPA server and the server
       gets re-installed then the client machine may still have a keyring
       entry for the old server. This can cause a redirect from the
       session URI to the negotiate one. As a rule, always clear the keyring
       when enrolling a new client.
    
    2. We save the NSS dbdir in the connection so that when creating a new
       session we can determine if we need to re-initialize NSS or not. Most
       of the time we do not. The dbdir was not always being preserved between
       connections which could cause an NSS_Shutdown() to happen which would
       fail because of existing usage. This preserves the dbdir information when
       a new connection is created as part of the session mechanism.
    
    https://fedorahosted.org/freeipa/ticket/3108