CBLT-245:  only show tails of xcodebuild outputs

Change-Id: Ia4e58b71470f6c259cfef528e7d7fa7da70741be
Reviewed-on: http://review.couchbase.org/35048
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>