Introduce some delay for sending "Connection refused" notifications

[wrygiel]

@mpuzar:

Hi Wojtek,

the monitoring thingy is nice, but possibly a bit too sensitive.
It sends a mail already after the first "java.net.ConnectException:
Connection refused", for which there could be many reasons... so I do get
occasional "false positives". Maybe it should try at least twice before
marking it as a problem? In our monitoring system the standard is 5 minutes
(that is, 5 tries).

Best,
Matija