[SPARK-18171][MESOS] Show correct framework address in mesos master web ui...

[SPARK-18171][MESOS] Show correct framework address in mesos master web ui when the advertised address is used

## What changes were proposed in this pull request?

In [SPARK-4563](https://issues.apache.org/jira/browse/SPARK-4563) we added the support for the driver to advertise a different hostname/ip (`spark.driver.host` to the executors other than the hostname/ip the driver actually binds to (`spark.driver.bindAddress`). But in the mesos webui's frameworks page, it still shows the driver's binds hostname/ip (though the web ui link is correct). We should fix it to make them consistent.

Before:

![mesos-spark](https://cloud.githubusercontent.com/assets/717363/19835148/4dffc6d4-9eb8-11e6-8999-f80f10e4c3f7.png)

After:

![mesos-spark2](https://cloud.githubusercontent.com/assets/717363/19835149/54596ae4-9eb8-11e6-896c-230426acd1a1.png)

This PR doesn't affect the behavior on the spark side, only makes the display on the mesos master side more consistent.
## How was this patch tested?

Manual test.
- Build the package and build a docker image (spark:2.1-test)

``` sh
./dev/make-distribution.sh -Phadoop-2.6 -Phive -Phive-thriftserver -Pyarn -Pmesos
```
-  Then run the spark driver inside a docker container.

``` sh
docker run --rm -it \
  --name=spark \
  -p 30000-30010:30000-30010 \
  -e LIBPROCESS_ADVERTISE_IP=172.17.42.1 \
  -e LIBPROCESS_PORT=30000 \
  -e MESOS_NATIVE_LIBRARY=/usr/local/lib/libmesos-1.0.0.so \
  -e MESOS_NATIVE_JAVA_LIBRARY=/usr/local/lib/libmesos-1.0.0.so \
  -e SPARK_HOME=/opt/dist \
  spark:2.1-test
```
- Inside the container, launch the spark driver, making use of the advertised address:

``` sh
/opt/dist/bin/spark-shell \
  --master mesos://zk://172.17.42.1:2181/mesos \
  --conf spark.driver.host=172.17.42.1 \
  --conf spark.driver.bindAddress=172.17.0.1 \
  --conf spark.driver.port=30001 \
  --conf spark.driver.blockManager.port=30002 \
  --conf spark.ui.port=30003 \
  --conf spark.mesos.coarse=true \
  --conf spark.cores.max=2 \
  --conf spark.executor.cores=1 \
  --conf spark.executor.memory=1g \
  --conf spark.mesos.executor.docker.image=spark:2.1-test
```
- Run several spark jobs to ensure everything is running fine.

``` scala
val rdd = sc.textFile("file:///opt/dist/README.md")
rdd.cache().count
```

Author: Shuai Lin <linshuai2012@gmail.com>

Closes #15684 from lins05/spark-18171-show-correct-host-name-in-mesos-master-web-ui.

mesos/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala

@@ -80,6 +80,8 @@ trait MesosSchedulerUtils extends Logging {
     frameworkId.foreach { id =>
       fwInfoBuilder.setId(FrameworkID.newBuilder().setValue(id).build())
     }
+    fwInfoBuilder.setHostname(Option(conf.getenv("SPARK_PUBLIC_DNS")).getOrElse(
+      conf.get(DRIVER_HOST_ADDRESS)))
     conf.getOption("spark.mesos.principal").foreach { principal =>
       fwInfoBuilder.setPrincipal(principal)
       credBuilder.setPrincipal(principal)