Don't check exit status when nc_client is spawned

In all cases where we are using nc_client, we rely on the messages
returned there in stdout and we don't really check exit_status codes.

It seems that e.g. ncat provided by RHEL 9 returns error_code=1 in case
when connection was refused. And that is expected thing e.g. in some
parts of the port_forwarding related tests.
To avoid unexpected failures due to ShellCommandFailed error we
shouldn't check exit_code there and always return messages from
nc_client's stdout to assert them in the test.

Closes: rhbz#2210233
Change-Id: I17cebaa34acb0dd6c60bd106eb70656faaebbb04
diff --git a/neutron_tempest_plugin/scenario/base.py b/neutron_tempest_plugin/scenario/base.py
index d972953..d03d726 100644
--- a/neutron_tempest_plugin/scenario/base.py
+++ b/neutron_tempest_plugin/scenario/base.py
@@ -638,8 +638,7 @@
         """
         cmd = get_ncat_client_cmd(ip_address, port, protocol,
                                   ssh_client=ssh_client)
-        result = shell.execute(cmd, ssh_client=ssh_client)
-        self.assertEqual(0, result.exit_status)
+        result = shell.execute(cmd, ssh_client=ssh_client, check=False)
         return result.stdout
 
     def _ensure_public_router(self, client=None, tenant_id=None):