sysdb: sanitize certmap rule name before using it in DN
    
    The name of a certificate mapping and matching rule might contain
    characters which are not allowed in RDNs an must be escaped before if
    can be used in the DN of the cached certmap object.
    
    Resolves: https://pagure.io/SSSD/sssd/issue/3721
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>