small tweaks and whitespace fixes

Most test databases are 16mb or maybe 48mb on disk (the first mongodb smallfile of 16mb + the second of 32mb). Having an oplog that is more than twice as large seems like overkill to me.

The 16mb document test is more of a mongodb test rather than a replica set test (we shouldn't be testing the mongodb server replication functionality right?) I guess we could make it 20mb so you could test that but 100mb is too much. We frequently spin up multiple 3 node sets in parallel so this can chew up disk fairly fast.