ROLE command added.

The new ROLE command is designed in order to provide a client with
informations about the replication in a fast and easy to use way
compared to the INFO command where the same information is also
available.
ROLE output improved for slaves.

Info about the replication state with the master added.
Cluster: cluster_my_epoch added to CLUSTER INFO output.
Cluster test: check master -> slave role switch.
Cluster test: unit 02 should wait for failover.
Cluster test: 02 unit more reliable waiting for slave sync.
Cluster test: new unit 03, failover loop stress testing.
Cluster test: added show-redis-logs command in the interactive console.
Cluster test: better failover detection in unit 03.
Cluster test: unit 03, check epochs correctness.
Cluster: log when a master denies a failover auth.
Cluster: log configEpoch updates to myself.
Cluster: log granted failover authorizations.
Cluster test: set config epochs when creating clusters.
Cluster: better comment for clusterSendFailoverAuthIfNeeded() epoch test.
Cluster: fix an error message when logging failover auth denied.
Scripting: Fix regression from #1118

The new check-for-number behavior of Lua arguments broke
users who use large strings of just integers.

The Lua number check would convert the string to a number, but
that breaks user data because
Lua numbers have limited precision compared to an arbitrarily
precise number wrapped in a string.

Regression fixed and new test added.

Fixes #1118 again.
Scripting: Fix for a #1118 regression simplified.

It is more straightforward to just test for a numerical type avoiding
Lua's automatic conversion. The code is technically more correct now,
however Lua should automatically convert to number only if the original
type is a string that "looks like a number", and not from other types,
so practically speaking the fix is identical AFAIK.
Cluster test: rewrite config when resetting nodes.
Cluser test: write multiple keys in unit 03.

The write-failover-read test is better if we write 100 keys so that we
are sure all the nodes are affected by the write.