CCBC-343: Fix environment variable handling for 'booleans'

Change-Id: Ied96696658c9828f6a555365afad43bd4cce5a7d
Reviewed-on: http://review.couchbase.org/34359
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>