Check whether we can stop a generic server without first asking it to
listen.
The test fails currently; the failure mode is a hang, which triggers the 5
minute timeout set in the test:
> unknown location(0): fatal error: in "stop_without_listening":
> seastar::timed_out_error: timedout
> seastar/src/testing/seastar_test.cc(43): last checkpoint
> test/boost/generic_server_test.cc(34): Leaving test case
> "stop_without_listening"; testing time: 300097447us
Signed-off-by: Laszlo Ersek <laszlo.ersek@scylladb.com>
