[build] Use DEPENDENCY_URL instead of CLOUDFRONT_URL_PREFIX
[build] Use DEPENDENCY_URL instead of CLOUDFRONT_URL_PREFIX

DEPENDENCY_URL is defined in vars.sh and defaults to CLOUDFRONT_URL_PREFIX.
CLOUDFRONT_URL_PREFIX is not used directly anywhere else.

Change-Id: I948ea2f87d497d6c752a012f2c166d3f9b25a065
Reviewed-on: http://gerrit.cloudera.org:8080/12713
Tested-by: Kudu Jenkins
Reviewed-by: Attila Bukor <53758272babe3057a5ff4ad51afd9bfd6e6014a1@apache.org>

helifu/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,InspurUSA/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,helifu/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu