by using for range loops
+ use returned iterator by erase call in ZConnectionPool

Change-Id: I97b14b24ebddefea909bc17cb3463f840fde38a0
Reviewed-on: https://gerrit.libreoffice.org/48634Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Tested-by: Julien Nabet <serval2412@yahoo.fr>