Add configuration to support broker SSL

Possibly implements #154, if my assumptions about the implementation are
correct.

broker.go

@@ -1,6 +1,7 @@
 package sarama
 
 import (
+	"crypto/tls"
 	"fmt"
 	"io"
 	"net"
@@ -12,7 +13,9 @@ import (
 
 // BrokerConfig is used to pass multiple configuration options to Broker.Open.
 type BrokerConfig struct {
-	MaxOpenRequests int // How many outstanding requests the broker is allowed to have before blocking attempts to send (default 5).
+	MaxOpenRequests int         // How many outstanding requests the broker is allowed to have before blocking attempts to send (default 5).
+	UseTLS          bool        // Whether or not to use TLS when connecting to the broker (defaults to false).
+	TLSConfig       *tls.Config // The TLS configuration to use for secure connections if specified by UseTLS (defaults to nil).
 
 	// All three of the below configurations are similar to the `socket.timeout.ms` setting in JVM kafka.
 	DialTimeout  time.Duration // How long to wait for the initial connection to succeed before timing out and returning an error (default 30s).
@@ -110,7 +113,15 @@ func (b *Broker) Open(conf *BrokerConfig) error {
 	go withRecover(func() {
 		defer b.lock.Unlock()
 
-		b.conn, b.connErr = net.DialTimeout("tcp", b.addr, conf.DialTimeout)
+		dialer := &net.Dialer{
+			Timeout: conf.DialTimeout,
+		}
+
+		if conf.UseTLS {
+			b.conn, b.connErr = tls.DialWithDialer(dialer, "tcp", b.addr, conf.TLSConfig)
+		} else {
+			b.conn, b.connErr = dialer.Dial("tcp", b.addr)
+		}
 		if b.connErr != nil {
 			b.conn = nil
 			atomic.StoreInt32(&b.opened, 0)