VOL-1670 - close and reestablish connections

When grpc connectivity to the core is broken the ofagent will
break the connection to ONOS and then work to reconnect to
the core. After connecting to the core the connection to
ONOS will be restablished.

Change-Id: I75e645de3784a64ef4f9992df8baf37959cbbd86
diff --git a/python/ofagent/probe.py b/python/ofagent/probe.py
index 612d661..1d2358e 100644
--- a/python/ofagent/probe.py
+++ b/python/ofagent/probe.py
@@ -15,11 +15,12 @@
 #
 from SimpleHTTPServer import SimpleHTTPRequestHandler
 from structlog import get_logger
-from connection_mgr import ConnectionManager
 log = get_logger()
 
 class Probe(SimpleHTTPRequestHandler):
 
+    connection_manager = None
+
     def do_GET(self):
 
         if self.path == '/healthz':
@@ -30,7 +31,7 @@
 
     def health_probe(self):
 
-        if ConnectionManager.liveness_probe():
+        if Probe.connection_manager is None or Probe.connection_manager.liveness_probe():
             self.send_response(200)
             self.end_headers()
         else :
@@ -39,7 +40,7 @@
 
     def ready_probe(self):
 
-        if ConnectionManager.readiness_probe():
+        if Probe.connection_manager is not None and Probe.connection_manager.readiness_probe():
             self.send_response(200)
             self.end_headers()
         else :