Support the manual master switch using the failover coordinator

[Totktonada]

Something like the following.

$ tt failover switch i-002 [--timeout 10] [-d]
<..here command updates are shown if -d is omitted..>

See https://github.com/tarantool/tarantool-ee/pull/759 for details.

[askalt]

Now, we have tt cluster replicaset promote/demote/expel. The commands patch the config in etcd to make some action.

How do you think, can we name it tt cluster replicaset switch?

[Totktonada]

I don't mind any solution, in fact.

However, I expect that there may be more commands related to failover coordinators and it may be convenient to have a namespace for them.

[oleg-jukovec]

So we decided:

tt cluster failover switch
tt cluster failover status
...