UTIL: Sanitize whitespaces.
    
    Original patches submitted by: mpesari(Thanks!!)
    
    It can cause problems if user will hit spaces before entering username.
    (e.g in gdm). Spaces are ignored by LDAP; it's better to escape them.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/1955
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    (cherry picked from commit 2b8208b45feb2aab64d560d3e12e01e7b6d00d39)