pmgspamreport: purge before sending reports

pmgspamreport: purge before sending reports

By cleaning the quarantine (database and files in spool directory), before
trying to send out mail we can prevent the file-system and database from
filling up because of an unrelated problem in sending out mails.

Originally discovered while analyzing why the quarantine spooldir on a
non-master node fills up, while being limted in size on the master-node:
the call to send out the reports errored out, because the node was not master.

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
Reviewed-By: Dominik Csapak <d.csapak@proxmox.com>