API: No HG mode switch if no selectors are present

If a hostgroup has no port selectors, then we do not allow to switch
over between infra and baremetal mode. These hostgroups are in infra
mode by default and will stay there, as we don't have all necessary
information to do the switch.

networking_aci/extensions/acioperations.py

@@ -180,6 +180,10 @@ def update(self, request, **kwargs):
         if not hg_config:
             raise web_exc.HTTPBadRequest("Hostgroup {} has no config associated with it".format(hostgroup_name))
 
+        if not hg_config.get('port_selectors'):
+            raise web_exc.HTTPBadRequest(f"Hostgroup {hostgroup_name} has no port selectors, "
+                                         "therefore hostgroup mode cannot be switched")
+
         if curr_mode == aci_const.MODE_BAREMETAL:
             # for baremetal switchover we need to check all baremetal segments for active portbindings
             physnet_to_check = "{}%".format(ACI_CONFIG.baremetal_resource_prefix)