Inconsistent postgres URI

The openflow-gec15 uses `postgres://SERVER/DB?user=USER&password=PASS`
for the PostGreSQL URI.

However, it is more customary to use `postgres://USER:PASS@SERVER:PORT/DB/PARAMS` [0], which is also what the rest of the OML stack uses.

[0] http://www.postgresql.org/docs/current/static/libpq-connect.html#AEN38155
