[SPARK-9633] [BUILD] SBT download locations outdated; need an update

Remove 2 defunct SBT download URLs and replace with the 1 known download URL. Also, use https.
Follow up on https://github.com/apache/spark/pull/7792

Author: Sean Owen <sowen@cloudera.com>

Closes #7956 from srowen/SPARK-9633 and squashes the following commits:

caa40bd [Sean Owen] Remove 2 defunct SBT download URLs and replace with the 1 known download URL. Also, use https.

build/sbt-launch-lib.bash

@@ -38,8 +38,7 @@ dlog () {
 
 acquire_sbt_jar () {
   SBT_VERSION=`awk -F "=" '/sbt\.version/ {print $2}' ./project/build.properties`
-  URL1=http://typesafe.artifactoryonline.com/typesafe/ivy-releases/org.scala-sbt/sbt-launch/${SBT_VERSION}/sbt-launch.jar
-  URL2=http://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/sbt-launch/${SBT_VERSION}/sbt-launch.jar
+  URL1=https://dl.bintray.com/typesafe/ivy-releases/org.scala-sbt/sbt-launch/${SBT_VERSION}/sbt-launch.jar
   JAR=build/sbt-launch-${SBT_VERSION}.jar
 
   sbt_jar=$JAR
@@ -51,12 +50,10 @@ acquire_sbt_jar () {
     printf "Attempting to fetch sbt\n"
     JAR_DL="${JAR}.part"
     if [ $(command -v curl) ]; then
-      (curl --fail --location --silent ${URL1} > "${JAR_DL}" ||\
-        (rm -f "${JAR_DL}" && curl --fail --location --silent ${URL2} > "${JAR_DL}")) &&\
+      curl --fail --location --silent ${URL1} > "${JAR_DL}" &&\
         mv "${JAR_DL}" "${JAR}"
     elif [ $(command -v wget) ]; then
-      (wget --quiet ${URL1} -O "${JAR_DL}" ||\
-        (rm -f "${JAR_DL}" && wget --quiet ${URL2} -O "${JAR_DL}")) &&\
+      wget --quiet ${URL1} -O "${JAR_DL}" &&\
         mv "${JAR_DL}" "${JAR}"
     else
       printf "You do not have curl or wget installed, please install sbt manually from http://www.scala-sbt.org/\n"