SEBA-542 Basic scaffolding for TT Workflow Driver service

Change-Id: Ia88a4d22f40b45299bb35e7bc5600cccbc453873
diff --git a/xos/synchronizer/event_steps/onu_event.py b/xos/synchronizer/event_steps/onu_event.py
new file mode 100644
index 0000000..386942f
--- /dev/null
+++ b/xos/synchronizer/event_steps/onu_event.py
@@ -0,0 +1,61 @@
+
+# Copyright 2017-present Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import json
+from xossynchronizer.event_steps.eventstep import EventStep
+
+class ONUEventStep(EventStep):
+    topics = ["onu.events"]
+    technology = "kafka"
+
+    max_onu_retry = 50
+
+    def __init__(self, *args, **kwargs):
+        super(ONUEventStep, self).__init__(*args, **kwargs)
+
+    def get_tt_si(self, event):
+        try:
+            tt_si = self.model_accessor.TtWorkflowDriverServiceInstance.objects.get(serial_number=event["serial_number"])
+            tt_si.no_sync = False;
+            tt_si.uni_port_id = event["uni_port_id"]
+            tt_si.of_dpid = event["of_dpid"]
+            self.log.debug("onu.events: Found existing TtWorkflowDriverServiceInstance", si=tt_si)
+        except IndexError:
+            # create an TtWorkflowDriverServiceInstance, the validation will be triggered in the corresponding sync step
+            tt_si = self.model_accessor.TtWorkflowDriverServiceInstance(
+                serial_number=event["serial_number"],
+                of_dpid=event["of_dpid"],
+                uni_port_id=event["uni_port_id"],
+                owner=self.model_accessor.TtWorkflowDriverService.objects.first() # we assume there is only one TtWorkflowDriverService
+            )
+            self.log.debug("onu.events: Created new TtWorkflowDriverServiceInstance", si=tt_si)
+        return tt_si
+
+    def process_event(self, event):
+        value = json.loads(event.value)
+        self.log.info("onu.events: received event", value=value)
+
+        if value["status"] == "activated":
+            self.log.info("onu.events: activated onu", value=value)
+            tt_si = self.get_tt_si(value)
+            tt_si.onu_state = "ENABLED"
+            tt_si.save_changed_fields(always_update_timestamp=True)
+        elif value["status"] == "disabled":
+            self.log.info("onu.events: disabled onu, not taking any action", value=value)
+            return
+        else:
+            self.log.warn("onu.events: Unknown status value: %s" % value["status"], value=value)
+            return