Make grainstore database name configuration explicit (#125)

Attempts to retrieve the `dbname` attribute without it being set
silently return nothing. This is problematic in scenarios where a
connection string is being built, and a missing database name defaults
to the UNIX username that initiated the connection attempt.

server.js

@@ -73,7 +73,8 @@ var windshaftConfig = {
             user: process.env.OTM_DB_USER || 'otm',
             password: process.env.OTM_DB_PASSWORD || 'otm',
             host: process.env.OTM_DB_HOST || 'localhost',
-            port: process.env.OTM_DB_PORT || 5432
+            port: process.env.OTM_DB_PORT || 5432,
+            dbname: dbname
         }
     }, // See grainstore npm for other options