Refactor error logging

It is hard to grep errors in current log. so in this patch,
I'm updating die function which also writes log for
screen_log_dir/error.log.
In future, we may categolize negative fault by using
this error.log.

Change-Id: I70a8cfe67ed408284f5c88c762c6bb8acb8ecdb2
diff --git a/lib/keystone b/lib/keystone
index a1a57f8..2580351 100644
--- a/lib/keystone
+++ b/lib/keystone
@@ -323,8 +323,7 @@
     screen_it key "cd $KEYSTONE_DIR && $KEYSTONE_DIR/bin/keystone-all --config-file $KEYSTONE_CONF $KEYSTONE_LOG_CONFIG -d --debug"
     echo "Waiting for keystone to start..."
     if ! timeout $SERVICE_TIMEOUT sh -c "while ! http_proxy= curl -s http://$SERVICE_HOST:$service_port/v2.0/ >/dev/null; do sleep 1; done"; then
-      echo "keystone did not start"
-      exit 1
+      die $LINENO "keystone did not start"
     fi
 
     # Start proxies if enabled