data race between test and product code in partition compaction

[davidby-influx]

There is an occasional data race between a test and the product code. The test needs to lock the partition for writing before modifying the MaxLogFileSize.

Failed
=== RUN   TestPartition_Compact_Write_Fail
=== RUN   TestPartition_Compact_Write_Fail/write_MANIFEST
==================
WARNING: DATA RACE
Write at 0x00c0001593e0 by goroutine 7789:
  github.com/influxdata/influxdb/tsdb/index/tsi1_test.TestPartition_Compact_Write_Fail.func1()
      /root/project/tsdb/index/tsi1/partition_test.go:135 +0x14a
  testing.tRunner()
      /go/src/testing/testing.go:1446 +0x216
  testing.(*T).Run.func1()
      /go/src/testing/testing.go:1493 +0x47

Previous read at 0x00c0001593e0 by goroutine 7790:
  github.com/influxdata/influxdb/tsdb/index/tsi1.(*Partition).needsLogCompaction()
      /root/project/tsdb/index/tsi1/partition.go:1217 +0x9e
  github.com/influxdata/influxdb/tsdb/index/tsi1.(*Partition).compact()
      /root/project/tsdb/index/tsi1/partition.go:1013 +0x19d
  github.com/influxdata/influxdb/tsdb/index/tsi1.(*Partition).Compact()
      /root/project/tsdb/index/tsi1/partition.go:915 +0x72
  github.com/influxdata/influxdb/tsdb/index/tsi1.(*Partition).runPeriodicCompaction()
      /root/project/tsdb/index/tsi1/partition.go:952 +0x47
  github.com/influxdata/influxdb/tsdb/index/tsi1.(*Partition).Open.func3()
      /root/project/tsdb/index/tsi1/partition.go:254 +0x39

Goroutine 7789 (running) created at:
  testing.(*T).Run()
      /go/src/testing/testing.go:1493 +0x75d
  github.com/influxdata/influxdb/tsdb/index/tsi1_test.TestPartition_Compact_Write_Fail()
      /root/project/tsdb/index/tsi1/partition_test.go:125 +0x44
  testing.tRunner()
      /go/src/testing/testing.go:1446 +0x216
  testing.(*T).Run.func1()
      /go/src/testing/testing.go:1493 +0x47

Goroutine 7790 (running) created at:
  github.com/influxdata/influxdb/tsdb/index/tsi1.(*Partition).Open()
      /root/project/tsdb/index/tsi1/partition.go:254 +0xd2b
  github.com/influxdata/influxdb/tsdb/index/tsi1_test.MustOpenPartition()
      /root/project/tsdb/index/tsi1/partition_test.go:163 +0x49
  github.com/influxdata/influxdb/tsdb/index/tsi1_test.TestPartition_Compact_Write_Fail.func1()
      /root/project/tsdb/index/tsi1/partition_test.go:129 +0xb4
  testing.tRunner()
      /go/src/testing/testing.go:1446 +0x216
  testing.(*T).Run.func1()
      /go/src/testing/testing.go:1493 +0x47
==================