Support for vrf on cumulus linux in puppet-network module

[TorLdre]

Starting with Cumulus linux 3 series, the NOS now supports VRFs. Also, it is recommended to create a management VRF to isolate the management network from the forwarding plane. In order to do so (as opposed to in Cumulus linux 2.x), one creates interface files in order to

1. Create VRFs themselves
2. Attach interfaces to VRFs created in (1)

I will create a PR that will facilitate the necessary changes.

Expected Behavior

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Actual Behavior

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Steps to Reproduce the Problem

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Specifications

Please add this info:
PR code tested in puppet 3.x and 4.x.