Add HashiCorp Nomad provider (#483)

* 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

vendor/github.com/armon/go-metrics/const_windows.go

@@ -0,0 +1,13 @@
+// +build windows
+
+package metrics
+
+import (
+	"syscall"
+)
+
+const (
+	// DefaultSignal is used with DefaultInmemSignal
+	// Windows has no SIGUSR1, use SIGBREAK
+	DefaultSignal = syscall.Signal(21)
+)