LDAP: Sanitize group dn before using in filter
Each string should be sanitized(rfc4515) before using ldbsearch.
A group dn was not sanitized in the function cleanup_groups.
Resolves:
https://fedorahosted.org/sssd/ticket/2744
Reviewed-by: Pavel Březina <pbrezina@redhat.com>
(cherry picked from commit 6cb5bad3c8e2f35ca9dce1800a506d626f90c079)
(cherry picked from commit 28dff998717b8bc70e28f39a8c7e3720c04305b7)