vpoller-cclient: Return EX_UNAVAILABLE if don't get a reply back
vPoller now requires vConnector version 0.2.9
Nuke keep_agents_alive() method

* https://github.com/dnaeon/py-vpoller/issues/45
Nuke start_vsphere_agents() method

* https://github.com/dnaeon/py-vpoller/issues/45
Remove leftovers