Redefine 'LOG(' macro to only expand level base argument once

Change-Id: I492d823465bad3d17650865138fdfb8f7fd38909
Reviewed-on: http://review.couchbase.org/38080
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>