mod-notify leaks a socket when performing POST /notify ..
Can be demonstrated in a unit test by repeated calls to POST /notify.
It is also clear from code inspection that a WebClient is constructed for calls to postNotify -> getOkapiModulesClient - > OkapiModulesClientImpl.
OkapiModulesClientImpl never closes webClient (not that it should, but better than creating a pool every time)
Instead OkapiModulesClientImpl should create only one WebClient per Vert.x instance.
Repeating test SendNotifyTest.testValidRequest is a way to reveal that number of sockets. Unfortunately, not so easy to
make a test for number of sockets in use.