Support vcenter only service chaining

Summary
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This feature will allow user to configure service-chaining (v2 only) in vCenter only mode of operation.
This feature will support in-network and in-network-nat service-chain.

Implementation details
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Service-chaining was not supported in vCenter-only mode as there needed support to spawn a ServiceVM on vCenter via Service-monitor. With portTuple (aka v2) way of
configuring service chain, it's possible to spawn a ServiceVM via vCenterUI and then stitch it
in a service-chain via contrail UI or by using vnc_api.

Modification are required in following modules to support this feature:
1) Contrail vCenter UI: Service-chain configuration was disabled in Contrail vCenter UI.
    It needs to enabled (v2 only).
2) Service-monitor: Service-monitor was disabled on vCenter-only contrail installation.
   It need to be installed and madee operational.