CLOUDSTACK-8375: Marvin - Code Improvement - Verifying VCenter port groups corresponding to traffic types in a zone

[gauravaradhye]

1. Reducing complexity of function "verifyVCenterPortGroups". Earlier it had two for loops, now it has only one. The parameter zone_list has been replaced with "zone" because we map a VCenter to a zone and not multiple zones.
2. Correcting the logic used to generate expected port group names for public traffic. The port group with network rate as defined in "network.throttling.rate" is created only when a VM is deployed and its network uses a public IP from public IP range dedicated to public traffic.
3. Adding a wrapper function for verifying guest traffic port groups which creates vcenter connection object and calls verifyVCenterPortGroups function with GUEST_TRAFFIC as parameter. This function is very handy and can be called from any networking test case with only a single line call. This separates the additional logic from test case and moves it to this wrapper function.

The code has been tested against multiple types of Vmware deployments including mixture tagged and untagged traffic types and mixed switches (SVS and DVS).

[srikanteswartalluri]

This is merged. forgot to add 'This closes #155'
Gaurav,
Please close this PR.