[SPARK-9633] [BUILD] SBT download locations outdated; need an update
[SPARK-9633] [BUILD] SBT download locations outdated; need an update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 <291c18f3fb7528c712d9098b0e50a515ea0b91d5@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.

(cherry picked from commit 681e3024b6c2fcb54b42180d94d3ba3eed52a2d4)
Signed-off-by: Sean Owen <291c18f3fb7528c712d9098b0e50a515ea0b91d5@cloudera.com>

andrewor14/iolap,andrewor14/iolap,andrewor14/iolap,andrewor14/iolap,andrewor14/iolap,andrewor14/iolap,andrewor14/iolap