MB-100 Tests should not assume deleted keys take 0 space
MB-100 Tests should not assume deleted keys take 0 space

space_used represents the amount of data in a file that is not "junk",
or that will be retained after compaction. Because metadata about
deleted items is kept around, a file with all the items that had been
present before will not have a space_used of 0

Change-Id: Ib41f55135ba739a91c08ec6866c84e8b782bf9ef
Reviewed-on: http://review.couchbase.org/20597
Reviewed-by: Jens Alfke <21e2afd93d5ce53123476032b5dca8a79b546094@couchbase.com>
Tested-by: Aaron Miller <41fcc51335f382e0855796cc35dd33f571f2d8f7@ninjawhale.com>

t3rm1n4l/couchstore,abhinavdangeti/couchstore,jimwwalker/couchstore,couchbaselabs/couchstore-specials,t3rm1n4l/couchstore,hsharsha/couchstore,couchbaselabs/couchstore-specials,couchbaselabs/couchstore,jimwwalker/couchstore,hsharsha/couchstore,vmx/couchstore,couchbaselabs/couchstore-specials,vmx/couchstore,jimwwalker/couchstore,abhinavdangeti/couchstore,vmx/couchstore,hsharsha/couchstore,couchbaselabs/couchstore-specials,couchbaselabs/couchstore,t3rm1n4l/couchstore,couchbaselabs/couchstore-specials,hsharsha/couchstore,abhinavdangeti/couchstore,couchbaselabs/couchstore