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/hashicorp/go-sockaddr/ifattr.go

@@ -0,0 +1,65 @@
+package sockaddr
+
+import (
+	"fmt"
+	"net"
+)
+
+// IfAddr is a union of a SockAddr and a net.Interface.
+type IfAddr struct {
+	SockAddr
+	net.Interface
+}
+
+// Attr returns the named attribute as a string
+func (ifAddr IfAddr) Attr(attrName AttrName) (string, error) {
+	val := IfAddrAttr(ifAddr, attrName)
+	if val != "" {
+		return val, nil
+	}
+
+	return Attr(ifAddr.SockAddr, attrName)
+}
+
+// Attr returns the named attribute as a string
+func Attr(sa SockAddr, attrName AttrName) (string, error) {
+	switch sockType := sa.Type(); {
+	case sockType&TypeIP != 0:
+		ip := *ToIPAddr(sa)
+		attrVal := IPAddrAttr(ip, attrName)
+		if attrVal != "" {
+			return attrVal, nil
+		}
+
+		if sockType == TypeIPv4 {
+			ipv4 := *ToIPv4Addr(sa)
+			attrVal := IPv4AddrAttr(ipv4, attrName)
+			if attrVal != "" {
+				return attrVal, nil
+			}
+		} else if sockType == TypeIPv6 {
+			ipv6 := *ToIPv6Addr(sa)
+			attrVal := IPv6AddrAttr(ipv6, attrName)
+			if attrVal != "" {
+				return attrVal, nil
+			}
+		}
+
+	case sockType == TypeUnix:
+		us := *ToUnixSock(sa)
+		attrVal := UnixSockAttr(us, attrName)
+		if attrVal != "" {
+			return attrVal, nil
+		}
+	}
+
+	// Non type-specific attributes
+	switch attrName {
+	case "string":
+		return sa.String(), nil
+	case "type":
+		return sa.Type().String(), nil
+	}
+
+	return "", fmt.Errorf("unsupported attribute name %q", attrName)
+}