l2 connection - supported aside service token

[ocobles]

Added support to create ecx/v3 l2 connections using a Fabric Service Token .

• Request field is primaryServiceToken
• Value is returned in the get connection by uuid in vendorToken
• Value is exposed in the client as ServiceToken
• This attribute is not supported in redundant connections API calls (secondary attributes), not even from the portal. To create a redundant connection, it will be required two connection requests, one for each service token

fix #2

[displague]

It would build reviewer confidence if these new fields were included in the spec (described at https://developer.equinix.com/catalog/buyerv3#operation/createConnectionUsingPOST and https://developer.equinix.com/catalog/buyerv3#operation/getConnectionByUuidUsingGET).

[displague]

Thanks for the updated tests and fixtures describing the new response field.