MB-100: fix ep_engine compilation errors/warnings (master branch)

Change-Id: I296fd1937e33588d8b862b421a2ec0ad2d532f06
Reviewed-on: http://review.couchbase.org/24582
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>