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/softlayer/softlayer-go/sl/errors.go

@@ -0,0 +1,49 @@
+/**
+ * Copyright 2016 IBM Corp.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package sl
+
+import "fmt"
+
+// Error contains detailed information about an API error, which can be useful
+// for debugging, or when finer error handling is required than just the mere
+// presence or absence of an error.
+//
+// Error implements the error interface
+type Error struct {
+	StatusCode int
+	Exception  string `json:"code"`
+	Message    string `json:"error"`
+	Wrapped    error
+}
+
+func (r Error) Error() string {
+	if r.Wrapped != nil {
+		return r.Wrapped.Error()
+	}
+
+	var msg string
+	if r.Exception != "" {
+		msg = r.Exception + ": "
+	}
+	if r.Message != "" {
+		msg = msg + r.Message + " "
+	}
+	if r.StatusCode != 0 {
+		msg = fmt.Sprintf("%s(HTTP %d)", msg, r.StatusCode)
+	}
+	return msg
+}