Util: Move socket setup in a common utility file
    
    Other components may need to connect sockets, the code here is generic enough
    that with minimal modifications can be used for non-ldap connections too.
    
    So create a sss_sockets.c/h utility file with all the non-ldap specific socket
    setup functions and make them available for other uses.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2968
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>