SYSDB: sysdb_get_bool() return ENOENT & unit tests
    
    sysdb_get_bool() return ENOENT if no result is found.
    Unit test for sysdb_get_bool() & sysdb_set_bool() was added.
    
    This patch also fixes ldap_setup_enumeration() to handle ENOENT returned by
    sysdb_has_enumerated().
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/1991
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>