New test, extends test_subport_connectivity

Related-Bug: #1869244

Adding new test, test_subport_connectivity_soft_reboot
The test is checking trunks and ports are recreated during server
reboots, especialy in ovs_dpdk ports,
Since test flow is variant of test_subport_connectivity
Two methods added and used in the tests:
_create_servers_with_trunk_port
_check_servers_remote_connectivity

Change-Id: Ia5fbe680bb904680f52e0e15056d629717a643af
diff --git a/neutron_tempest_plugin/config.py b/neutron_tempest_plugin/config.py
index 3812383..36fec30 100644
--- a/neutron_tempest_plugin/config.py
+++ b/neutron_tempest_plugin/config.py
@@ -97,6 +97,9 @@
     cfg.IntOpt('ssh_proxy_jump_port',
                default=22,
                help='Port used to connect to "ssh_proxy_jump_host".'),
+    cfg.IntOpt('reboots_in_test',
+               default=1,
+               help='Number of reboots to apply if tests requires reboots'),
 
     # Options for special, "advanced" image like e.g. Ubuntu. Such image can be
     # used in tests which require some more advanced tool than available in