[SPARK-1041] remove dead code in start script, remind user to set that in spark-env.sh

the lines in start-master.sh and start-slave.sh no longer work

in ec2, the host name has changed, e.g.

ubuntu@ip-172-31-36-93:~$ hostname
ip-172-31-36-93

also, the URL to fetch public DNS name also changed, e.g.

ubuntu@ip-172-31-36-93:~$ wget -q -O - http://instance-data.ec2.internal/latest/meta-data/public-hostname
ubuntu@ip-172-31-36-93:~$  (returns nothing)

since we have spark-ec2 project, we don't need to have such ec2-specific lines here, instead, user only need to set in spark-env.sh

Author: CodingCat <zhunansjtu@gmail.com>

Closes #588 from CodingCat/deadcode_in_sbin and squashes the following commits:

e4236e0 [CodingCat] remove dead code in start script, remind user set that in spark-env.sh

conf/spark-env.sh.template

@@ -19,3 +19,4 @@
 # - SPARK_WORKER_PORT / SPARK_WORKER_WEBUI_PORT
 # - SPARK_WORKER_INSTANCES, to set the number of worker processes per node
 # - SPARK_WORKER_DIR, to set the working directory of worker processes
+# - SPARK_PUBLIC_DNS, to set the public dns name of the master

sbin/start-master.sh

@@ -40,13 +40,4 @@ if [ "$SPARK_MASTER_WEBUI_PORT" = "" ]; then
   SPARK_MASTER_WEBUI_PORT=8080
 fi
 
-# Set SPARK_PUBLIC_DNS so the master report the correct webUI address to the slaves
-if [ "$SPARK_PUBLIC_DNS" = "" ]; then
-    # If we appear to be running on EC2, use the public address by default:
-    # NOTE: ec2-metadata is installed on Amazon Linux AMI. Check based on that and hostname
-    if command -v ec2-metadata > /dev/null || [[ `hostname` == *ec2.internal ]]; then
-        export SPARK_PUBLIC_DNS=`wget -q -O - http://instance-data.ec2.internal/latest/meta-data/public-hostname`
-    fi
-fi
-
 "$sbin"/spark-daemon.sh start org.apache.spark.deploy.master.Master 1 --ip $SPARK_MASTER_IP --port $SPARK_MASTER_PORT --webui-port $SPARK_MASTER_WEBUI_PORT

sbin/start-slave.sh

@@ -23,13 +23,4 @@
 sbin=`dirname "$0"`
 sbin=`cd "$sbin"; pwd`
 
-# Set SPARK_PUBLIC_DNS so slaves can be linked in master web UI
-if [ "$SPARK_PUBLIC_DNS" = "" ]; then
-    # If we appear to be running on EC2, use the public address by default:
-    # NOTE: ec2-metadata is installed on Amazon Linux AMI. Check based on that and hostname
-    if command -v ec2-metadata > /dev/null || [[ `hostname` == *ec2.internal ]]; then
-        export SPARK_PUBLIC_DNS=`wget -q -O - http://instance-data.ec2.internal/latest/meta-data/public-hostname`
-    fi
-fi
-
 "$sbin"/spark-daemon.sh start org.apache.spark.deploy.worker.Worker "$@"