This makes the concept of a `Provider` wholely implemented in the cli
implementation in cmd/virtual-kubelet.
It allows us to slim down the interfaces used in vkubelet (and
vkubelet/api) to what is actually used there rather than a huge
interface that is only there to serve the CLI's needs.
* provider: adding Nomad provider
* updating CONTRIBUTING.md with Nomad provider
* updated README.md by adding the Nomad provider
* fix typo
* adding nomad/api and nomad/testutil deps
* adding Nomad binary dependency for provider tests
* fixed the nomad binary download command step and added tolerations to the nomad provider.
* adding nomad provider demo gif
* adding my name to authors
* adding two missing go-rootcerts files after dep ensure
* delete pod comment
