Fixes attributes for mem in environment_config.yaml
Fixes attributes for mem in environment_config.yaml

This patch fixes the 'type' value for MEM attributes in
environment_config to prevent it to give errors when a new OpenStack
environment is created from the Fuel web UI.

Change-Id: I0430b209ee90ce981f383d483ec6142f31cc6fc9
Closes-bug: #1506144

stackforge/fuel-plugin-midonet,stackforge/fuel-plugin-midonet