MB-25746: Fix data race in store_test
MB-25746: Fix data race in store_test

==================
WARNING: DATA RACE
Read at 0x00c4200754a0 by goroutine 70:
  moss.TestStoreCrashRecovery.func1() moss/store_test.go:2053 +0x94
  moss.(*collection).fireEvent() moss/collection.go:531 +0xd6
  moss.(*collection).runPersister() moss/persister.go:131 +0x93e

Previous write at 0x00c4200754a0 by goroutine 53:
  moss.TestStoreCrashRecovery() moss/store_test.go:2131+0xc3c
  testing.tRunner()

Change-Id: Ieeee9b4e0f597ab0ea285a8a143e3ca2b9afec55
Reviewed-on: http://review.couchbase.org/82704
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>
Tested-by: Sundararaman Sridharan <333a3f71d3ad6e01fc953c4fa06bc1f3cd014910@couchbase.com>

couchbaselabs/moss