KUDU-2982: Document taking backups on earlier versions of Kudu
KUDU-2982: Document taking backups on earlier versions of Kudu

Adds a section to the backup documentation describing how to
succesfully take backups on Kudu clusters earlier than Kudu 1.10.

Change-Id: I15201bafc5c0e40b230873f92790d4fc2a02bdde
Reviewed-on: http://gerrit.cloudera.org:8080/14525
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Tested-by: Kudu Jenkins

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