LDAP: Move sdap_create_search_base from ldap to sdap code
    
    The function shouldn't be placed in the LDAP tree, but in the SDAP tree
    to make it usable from tests without linking to libraries that are
    normally linked from LDAP provider (such as confdb)
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>