Add SoftLayer DNS provider (#59)

Add SoftLayer DNS as a DomainServiceProvider.

The SoftLayer API is a bit of a mess and treats MX and SRV records
differently. This leads to some replication and custom handling issues
to work around.

In this patch I have to change the SRV test case to be _tcp instead of
_protocol because softlayer requires a "known" protocol which AFAICT is
tcp, udp or tls. I think this will be acceptable in most cases.

Signed-off-by: Jamie Lennox <jamielennox@gmail.com>

vendor/github.com/renier/xmlrpc/request.go

@@ -0,0 +1,57 @@
+package xmlrpc
+
+import (
+	"bytes"
+	"fmt"
+	"net/http"
+)
+
+func NewRequest(url string, method string, args interface{}) (*http.Request, error) {
+	var t []interface{}
+	var ok bool
+	if t, ok = args.([]interface{}); !ok {
+		if args != nil {
+			t = []interface{}{args}
+		}
+	}
+
+	body, err := EncodeMethodCall(method, t...)
+	if err != nil {
+		return nil, err
+	}
+
+	request, err := http.NewRequest("POST", url, bytes.NewReader(body))
+	if err != nil {
+		return nil, err
+	}
+
+	request.Header.Set("Content-Type", "text/xml")
+	request.Header.Set("Content-Length", fmt.Sprintf("%d", len(body)))
+
+	return request, nil
+}
+
+func EncodeMethodCall(method string, args ...interface{}) ([]byte, error) {
+	var b bytes.Buffer
+	b.WriteString(`<?xml version="1.0" encoding="UTF-8"?>`)
+	b.WriteString(fmt.Sprintf("<methodCall><methodName>%s</methodName>", method))
+
+	if args != nil {
+		b.WriteString("<params>")
+
+		for _, arg := range args {
+			p, err := marshal(arg)
+			if err != nil {
+				return nil, err
+			}
+
+			b.WriteString(fmt.Sprintf("<param>%s</param>", string(p)))
+		}
+
+		b.WriteString("</params>")
+	}
+
+	b.WriteString("</methodCall>")
+
+	return b.Bytes(), nil
+}