Add 'sessionId' into privet/info

Current implementation is a Unix timestamp plus counter.

BUG=26140026

Change-Id: Idfe0aa81c49e6dab5d638cbedfbeb460b70b5864
Reviewed-on: https://weave-review.googlesource.com/2010
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
diff --git a/src/privet/privet_handler_unittest.cc b/src/privet/privet_handler_unittest.cc
index fcbd0d0..c4180b9 100644
--- a/src/privet/privet_handler_unittest.cc
+++ b/src/privet/privet_handler_unittest.cc
@@ -247,7 +247,8 @@
       'id': '',
       'status': 'disabled'
     },
-    'time': 1410000001000.0
+    'time': 1410000001000.0,
+    'sessionId': 'SessionId'
   })";
   EXPECT_JSON_EQ(kExpected, HandleRequest("/privet/info", "{}"));
 }
@@ -308,7 +309,8 @@
       'id': 'TestCloudId',
       'status': 'online'
     },
-    'time': 1410000001000.0
+    'time': 1410000001000.0,
+    'sessionId': 'SessionId'
   })";
   EXPECT_JSON_EQ(kExpected, HandleRequest("/privet/info", "{}"));
 }