Zabbix

........S. [ZBXNEXT-4002] handle re-tries better.

The patch fix the excessive flooding of messages in the log
by controlling request re-tries in a bit more granular way.
In particular, we take care of reporting the current error
only once for every curl handle, put the handle in a retry
list and complete the loop.
Once done, we check if the retry list is not empty, if so, we
put the handles present bach in the multi handle and jump,
after ZBX_HISTORY_STORAGE_DOWN / 1000 (actually 10
seconds), to the beginning of the loop for trying to send data
again. In this way we always report for handles that are not
completed and properly pause between retries.