[IOTMID-220] Fixing mongodb image for SELinux

Current public docker of mongodb has an issue with SELinux -
it won't spawn child processes using the default user (root) -
as described here: docker-library/mongo#158

Apparently setting the user as 'mongodb' fixed this issue (or
disabling SELinux altogether, but this might be a major concern)

Change-Id: I8564b5211a5296606f5d4ede8d7fe2dffecb1524

Author: Giovanni Curiel dos Santos

docker-compose.yml

@@ -18,6 +18,7 @@ services:
 
   mongodb:
     image: "mongo:3.2"
+    user: "mongodb"
     networks:
       subs:
         aliases: