Commit [1] introduced an entry for reference vpn agent in cmd/eventlet module
so that they get monkey patched in an uniform way. This commit introduces the
same for vyatta vpn agent.
[1] I2d7081dbd4cb532332e3b66667bb8c71aa5a6658
Change-Id: Icc3c8f040bd4fbb2ad36e3d32a381a7ba7993d53
Closes-Bug: 1434337