FGCP driver returns error when retrieving load balancer with no instances, FW missing description, FW rules should exclude 'Deny' rules until DC API supports it, instance creation [Additional parameters] do not apply

Various issues with FGCP driver on my todo list or uncovered during internal review:

1. FW description should be descriptive
2. DC API does not distinguish between Accept and Deny rules, so omit Deny rules until DC API supports them
3. Error when retrieving details of a load balancer with no attached instances (nil check missing)
4. [Additional parameters] expandable field for instance creation should only be displayed if the driver supports any additional parameters (FGCP does not).