Add path and stream to dimensions if they exists

In Docker environment path is not setup but logs could be accuired from
STDOUT stream.

Change-Id: I755fa3d72bb81b61a4fa083fd974735bb13e4295

Author: matrixik

lib/logstash/outputs/monasca_log_api.rb

@@ -140,14 +140,18 @@ def encode(event)
 
   def generate_log_from_event(event)
     message = event.to_hash['message']
-    path = event.to_hash['path']
+    path = event.to_hash['path'] if event.to_hash['path']
+    stream = event.to_hash['stream'] if event.to_hash['stream']
     local_dims = JSON.parse(event.to_hash['dimensions'].to_s) if
       event.to_hash['dimensions']
     type = event.to_hash['type'] if event.to_hash['type']
     cross_tenant = event.to_hash['cross_tenant'] if
       event.to_hash['cross_tenant']
 
-    log = { 'message' => message, 'dimensions' => { 'path' => path }}
+    log = { 'message' => message, 'dimensions' => {} }
+    path && log['dimensions']['path'] = path
+    stream && log['dimensions']['stream'] = stream
+
     log[JSON_DIMS]['type'] = type if type
     if local_dims
       begin