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
```
This makes sure that when SSL is enabled (for FS/single node mode),
the server address is picked up from the --address option (that needs
to include the hostname for SSL verification, and has to be input
appropriately by user), instead of just using ":<port>".
In a distributed setup that the server should not perform any operation
on the storage layer after it is exported via RPC. e.g, cleaning up of
temporary directories under .minio.sys/tmp may interfere with ongoing
PUT objects being served by the distributed setup.
In a multipart upload scenario disks going down and coming backup
can lead to certain parts missing on the disk/server which was
going down. This is a valid case since these blocks can be
missing and should be healed through heal operation. But we are
not supposed to fail prematurely since we have enough data on
the other disks as well within read-quorum.
This fix relaxes previous assumption, fixes a major corruption
issue reproduced by @vadmeste.
Fixes#2976
Don't close socket while re-initializing notify-listeners, as the rpc
client object is shared between notify-listeners and peer clients.
Also, improves SendRPC() readability by using GetPeerClient().
Fixes a serialisation bug - encoding/gob does not directly support
serializing `map[string]interface{}`, so we serialise to JSON and send a
byte array in the RPC call, and deserialize and update on the receiver.
Karthic Rao