redis-trib: fixed type has_flags? -> has_flag.
redis-trib: added some more output for check.
redis-trib: fixed ClusterNode migrating/importing slots detection.
redis-trib: added cluster_error method to add errors.
redis-trib: fix open slot correction.

Slot zero was hardcoded (!)
redis-trib: All output wrapped by a specific function.

This is needed in order to colorize it as next step.
We use conventions in output messages such as

>>> This is an action
*** This is a warning
[ERR] This is an error
[OK] That's fine

And so forth, so that a color will be associated checking the first
three chars.
redis-cli --stat, stolen from redis-tools.

Redis-tools is a connection of tools no longer mantained that was
intented as a way to economically make sense of Redis in the pre-vmware
sponsorship era. However there was a nice redis-stat utility, this
commit imports one of the functionalities of this tool here in redis-cli
as it seems to be pretty useful.

Usage: redis-cli --stat

The output is similar to vmstat in the format, but with Redis specific
stuff of course.

From the point of view of the monitored instance, only INFO is used in
order to grab data.