db: TestCleaner fails under the race build on master on linux

[bananabrick]

arjunnair@gceworker-arjunnair:~/go/src/github.com/cockroachdb/pebble$ git branch
* master
  ve_enc_dec
arjunnair@gceworker-arjunnair:~/go/src/github.com/cockroachdb/pebble$ go test -race -exec 'stress' -run ^TestCleaner$

--- FAIL: TestCleaner (0.02s)
    datadriven.go:143: 
        testdata/cleaner:196:
         
        output didn't match expected:
        @@ -33,6 +33,10 @@
         remove: db1_wal/000002.log
         remove: db1_wal/000004.log
         remove: db1/000123.sst
         remove: db1/000456.sst
         remove: db1/OPTIONS-000003
        +open: db1/000005.sst
        +read-at(744, 53): db1/000005.sst
        +read-at(707, 37): db1/000005.sst
        +read-at(79, 628): db1/000005.sst
         
FAIL


ERROR: exit status 1

1 runs completed, 1 failures, over 0s
context canceled
FAIL
exit status 1
FAIL    github.com/cockroachdb/pebble   0.074s

This started failing more regularly due to #2484, but either way, it exists on master.

[RaduBerinde]

The extra open is coming from maybeCollectTableStatsLocked()