Merge from master (#328)

* Add default provider taint and taint configuration options

This allows for more specificity when setting taint tolerations for
workloads. Three new env variables are introduced:

VKUBELET_TAINT_KEY (defaults to `virtual-kubelet.io/provider`)
VKUBELET_TAINT_VALUE (defaults to provider name)
VKUBELET_TAINT_EFFECT (defaults to `NoSchedule`)

BREAKING CHANGES:
- The default taint key of `azure.com/aci` is now
  `virtual-kubelet.io/provider`.
- Specifying a custom taint key is now done via an environment variable
  rather than the `--taint` command line flag.

* Add back deprecated taint flag

TODO: Revert this commit

Related to #316

* Add darwin tag to not build for osx

* Darwin specific lookup file without cri and vic

* Fix chart notes template (#317)

Values were moved from env to top level.

* If --taint is specified, set the taint value to empty (#322)

Add the old tolerations the examples to make it backward compatible during the switch

* Use standard logging package (#323)

* Update kubelet vendor to pull in stats API

* Add errgroup dep which will be used for ACI stats

* Add supports for stats in ACI provider

This adds a new, optional, interface for providers that want to provide
stats.

* Don't use globals for API server

Refactors how HTTP servers are started and binds them to objects that
can store the provider rather than relying on a global.

* Fix merge conflict

* Fix couple errors

cmd/root.go

@@ -52,7 +52,7 @@ This allows users to schedule kubernetes workloads on nodes that aren't running
 	Run: func(cmd *cobra.Command, args []string) {
 		f, err := vkubelet.New(nodeName, operatingSystem, kubeNamespace, kubeConfig, provider, providerConfig, taintKey, disableTaint, metricsAddr)
 		if err != nil {
-			log.L.WithError(err).Fatal("Error initializing vritual kubelet")
+			log.L.WithError(err).Fatal("Error initializing virtual kubelet")
 		}
 		if err := f.Run(context.Background()); err != nil {
 			log.L.Fatal(err)