Currently we start a transaction that performs modifications to documents with snapshot read concern.

With snapshot read concern, we set the readSource to be the kAllCommittedSnapshot. This can cause build failures in the case where in our evergreen runs, an HMAC key insertion right before we prepopulate our test collection. In this case, since we prepopulate the collection while the WT transaction for the HMAC key insertion is not yet committed, the documents we insert into the test collection never make it into the all committed snapshot. This will cause inconsistencies in our test results. We should pin the committedSnapshot to always be <= allCommitted and also audit all uses of transactions with snapshot read concern to make sure any previous writes outside the transaction that are depended on by the transaction should be using majority write concern.