Document the need to re-download the repository list file to upgrade on Ubuntu
Document the need to re-download the repository list file to upgrade on Ubuntu

Change-Id: If342b3c820d1acb16e45ab3e9155565559b51075
Reviewed-on: http://gerrit.cloudera.org:8080/2530
Tested-by: Kudu Jenkins
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>

helifu/kudu,EvilMcJerkface/kudu,cloudera/kudu,helifu/kudu,helifu/kudu,andrwng/kudu,EvilMcJerkface/kudu,cloudera/kudu,andrwng/kudu,helifu/kudu,cloudera/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,andrwng/kudu,EvilMcJerkface/kudu,andrwng/kudu,EvilMcJerkface/kudu,cloudera/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,helifu/kudu,cloudera/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,andrwng/kudu,InspurUSA/kudu,cloudera/kudu,helifu/kudu,InspurUSA/kudu,cloudera/kudu,andrwng/kudu,cloudera/kudu,andrwng/kudu,InspurUSA/kudu,cloudera/kudu,andrwng/kudu,InspurUSA/kudu,InspurUSA/kudu,andrwng/kudu,InspurUSA/kudu,helifu/kudu