Adds property based testing framework for our compaction testings.
Current we support checking for "gaps" within adjacent compaction groups.

For example:
```
			expectedResult: func() TestLevelResults {
				return TestLevelResults{
					// Our rogue level 2 file should be picked up in the full compaction
					level4Groups: []tsm1.PlannedCompactionGroup{
						{
							tsm1.CompactionGroup{
								"000016844-000000002.tsm",
								"000016948-000000004.tsm",
								"000016948-000000005.tsm",
								"000017076-000000004.tsm",
								"000017094-000000004.tsm",
							},
							tsdb.DefaultMaxPointsPerBlock,
						},
					},
					// Other files should get picked up by optimize compaction
					level5Groups: []tsm1.PlannedCompactionGroup{
						{
							tsm1.CompactionGroup{
								"000016684-000000007.tsm",
								"000016684-000000008.tsm",
								"000016684-000000009.tsm",
								"000016684-000000010.tsm",
								"000016812-000000004.tsm",
								"000016812-000000005.tsm",
								"000017095-000000005.tsm",
							},
							tsdb.DefaultMaxPointsPerBlock,
						},
					},
				}
			},
		},
```

Would be invalid and cause our validator to fail due to the file `"000017095-000000005.tsm"` in `level5Groups`.

(cherry picked from commit 3f1f4a0)