[SPARK-4260] Httpbroadcast should set connection timeout.

Httpbroadcast sets read timeout but doesn't set connection timeout.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #3122 from sarutak/httpbroadcast-timeout and squashes the following commits:

c7f3a56 [Kousuke Saruta] Added Connection timeout for Http Connection to HttpBroadcast.scala

core/src/main/scala/org/apache/spark/broadcast/HttpBroadcast.scala

@@ -191,10 +191,12 @@ private[broadcast] object HttpBroadcast extends Logging {
       logDebug("broadcast security enabled")
       val newuri = Utils.constructURIForAuthentication(new URI(url), securityManager)
       uc = newuri.toURL.openConnection()
+      uc.setConnectTimeout(httpReadTimeout)
       uc.setAllowUserInteraction(false)
     } else {
       logDebug("broadcast not using security")
       uc = new URL(url).openConnection()
+      uc.setConnectTimeout(httpReadTimeout)
     }
 
     val in = {