scylla_coredump_setup: avoid coredump failure when hard limit of coredump is set to zero

On the environment hard limit of coredump is set to zero, coredump test
script will fail since the system does not generate coredump.
To avoid such issue, set ulimit -c 0 before generating SEGV on the script.

Note that scylla-server.service can generate coredump even ulimit -c 0
because we set LimitCORE=infinity on its systemd unit file.

Fixes #8238

Closes #8245

(cherry picked from commit af8eae317b)

dist/common/scripts/scylla_coredump_setup

@@ -87,7 +87,8 @@ WantedBy=multi-user.target
             run('sysctl -p /etc/sysctl.d/99-scylla-coredump.conf')
 
         fp = tempfile.NamedTemporaryFile()
-        fp.write(b'kill -SEGV $$')
+        fp.write(b'ulimit -c unlimited\n')
+        fp.write(b'kill -SEGV $$\n')
         fp.flush()
         p = subprocess.Popen(['/bin/bash', fp.name], stdout=subprocess.PIPE)
         pid = p.pid