CBLT-170:  only show tail of (zip) log files

Change-Id: I4e073f618779986f6894c91ee0267ac4b453a46a
Reviewed-on: http://review.couchbase.org/38162
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>