Remove trailing spaces from cluster.c file.
CLUSTER RESET implemented.

The new command is able to reset a cluster node so that it starts again
as a fresh node. By default the command performs a soft reset (the same
as calling it as CLUSTER RESET SOFT), and the following steps are
performed:

1) All slots are set as unassigned.
2) The list of known nodes is flushed.
3) Node is set as master if it is a slave.

When an hard reset is performed with CLUSTER RESET HARD the following
additional operations are performed:

4) A new Node ID is created at random.
5) Epochs are set to 0.

CLUSTER RESET is useful both when the sysadmin wants to reconfigure a
node with a different role (for example turning a slave into a master)
and for testing purposes.

It also may play a role in automatically provisioned Redis Clusters,
since it allows to reset a node back to the initial state in order to be
reconfigured.
Fixed typo in CLUSTER RESET implementation.
Cluster: clear todo_before_sleep flags when executing actions.

Thanks to this change, when there is some code like:

    clusterDoBeforeSleep(CLUSTER_TODO_UPDATE_STATE|...);
    ... and later before returning to the event loop ...
    clusterUpdateState();

The clusterUpdateState() function will clar the flag and will not be
repeated in the clusterBeforeSleep() function. This especially important
for config save/fsync flags which are slow to execute and not a good
idea to repeat without a good reason.

This is implemented for all the CLUSTER_TODO flags.
Cluster: use clusterSetNodeAsMaster() during slave failover.

clusterHandleSlaveFailover() was reimplementing what
clusterSetNodeAsMaster() without any good reason.