Add distributed firewall for NSX-V VDC

[dataclouder]

Functionalities added:

• Check whether the Distributed Firewall service is enabled;
• Enable Distributed Firewall service;
• Remove Distributed Firewall service
• Retrieve firewall rules
• Retrieve firewall services and service groups
• Add and update firewall rules
• Test for the above

Note 1: as per product specification, this PR only deals with layer 3 firewall rules.

Note 2: Adding and updating rules is the same operation:

• Both are added using a single PUT operation
• Every PUT rewrites the whole rule set
• Rule IDs are not considered when updating. The new rules, as indicated by the user, replace the old ones.
• The ID of the rules section (a section is either a "level2" or "level3" collection of rules) stays unchanged, unless the firewall is created again.

[Didainius]

First scan

[adambarreiro]

LGTM!