Added clear subcommand for control lock with following options:
```
3. Clear lock named 'bucket/object' (exact match).
$ minio control lock clear http://localhost:9000/bucket/object
4. Clear all locks with names that start with 'bucket/prefix' (wildcard match).
$ minio control lock --recursive clear http://localhost:9000/bucket/prefix
5. Clear all locks older than 10minutes.
$ minio control lock --older-than=10m clear http://localhost:9000/
6. Clear all locks with names that start with 'bucket/a' and that are older than 1hour.
$ minio control lock --recursive --older-than=1h clear http://localhost:9000/bucket/a
```
- Instrumentation for locks.
- Detailed test coverage.
- Adding RPC control handler to fetch lock instrumentation.
- RPC control handlers suite tests with a test RPC server.
Frank