In the following commits it'll be allowed to use names instead of
UUIDs. This patch refactors error module, changing the name of
arguments, accepted by errors: from now on it may be either UUID or
persistent name, so we cannot say, that this is always UUID, as it's
done now.

The alternative would be to rename arguments according to the
configuration used on the fly. It's not selected, as it complicates
expluatation.

Note, that this is breaking change, if user's code relies on UUID
arguments of returned errors!

Part of tarantool#426

NO_DOC=refactoring

This commit replaces all appearances of UUIDs in replicaset's
code, where it's possible to do without any functional changes.
This commit has only code-readability purpose, as in the future
named identification will be introduced.

Part of tarantool#426

NO_DOC=refactoring
NO_TEST=refactoring

From now on keys inside replicaset and replicaset.replicas may be either
replicaset/instance_name or UUID, depending on cfg.identification_mode.
We cannot use UUIDs always now, as they might not be specified at all.

Part of tarantool#426

NO_DOC=internal

Part of tarantool#426

@TarantoolBot document
Title: vshard: config identification mode

The option `identification_mode` should be specified in the root of the
config. It can have one of those values:

* `'uuid_as_key'` - default. Means, that default uuid config
    identification is used. replica.name is allowed and should not be
    interpreted as `box.cfg.instance_name`. replica/replicaset.uuid is
    forbidden. The config should have the following format:
    ```
    {
        ['cbf06940-0790-498b-948d-042b62cf3d29'] = { -- replicaset tarantool#1
            replicas = {
                ['8a274925-a26d-47fc-9e1b-af88ce939412'] = {
                    name = 'storage_1_a',
                    ...
                },
                ...
            },
        },
        ...
    }
    ```

* `'name_as_key'`. Name identification is used, supported only by
    Tarantool >= 3.0.0. It's forbidden to specify replica.name in
    such format. UUIDs are optional and can be specified via
    replicaset/replica.uuid:
    ```
    {
        replicaset_1 = {
            uuid = 'cbf06940-0790-498b-948d-042b62cf3d29',
            replicas = {
                replica_1_a = {
                    uuid = '8a274925-a26d-47fc-9e1b-af88ce939412'
                    ...
                },
                ...
            }
        },
        ...
    }
    ```

    Note, that names, used as keys in config are passed to
    box.cfg.replicaset/instance_name for storage. In case of
    reconfiguration it's strictly validated, that both
    replicaset and instance name corresponds to the passed
    config. Vshard doesn't deal with changing or setting names,
    it must be done externally (using Tarantool's config module,
    for example).

This commit replaces all appearances of UUIDs in storage's
code, where it's possible to do without any functional changes.
This commit has only code-readability purpose, as in the future
named identification will be introduced.

Part of tarantool#426

NO_DOC=refactoring
NO_TEST=refactoring

When named config is used, there may be no UUIDs specified for
replicas and replicasets. Consequently, in such case we must
also show the names in addition to UUIDs in storage.info().

Part of tarantool#426

@TarantoolBot document
Title: vshard: vshard.storage.info shows name

When `identification_mode` is `name_as_key`, persisted master and
replicaset name is shown in vshard.storage.info:

```
tarantool> vshard.storage.info()
---
- replicasets:
    replicaset_1:
      name: replicaset_1
      master:
        uri: admin@localhost:3302
        name: replica_1_a
  ...
```

This commit replaces all appearances of UUIDs in router's
code, where it's possible to do without any functional changes.
This commit has only code-readability purpose, as in the future
named identification will be introduced.

Part of tarantool#426

NO_DOC=refactoring
NO_TEST=refactoring

This commit allows router to use named config identification.

Part of tarantool#426

NO_DOC=<no API changed>

When named config is used, there may be no UUIDs specified for
replicas. Consequently, in such case we must also show the name
of replica, where bucket is located, not only UUID.

Part of tarantool#426

@TarantoolBot document
Title: vshard: vshard.router.buckets_info shows name

When `identification_mode` is `name_as_key`, buckets_info()
also returns name of the replicas, where buckets are stored:

```
tarantool> vshard.router.buckets_info()
---
- - uuid: aaaaaaaa-0000-4000-a000-000000000000
    status: available_rw
    name: replica_1_a
```

When named config is used, there may be no UUIDs specified for
replicas and replicasets. Consequently, in such case we must
also show the names in addition to UUIDs in router.info().

Part of tarantool#426

@TarantoolBot document
Title: vshard: vshard.router.info shows name

When `identification_mode` is `name_as_key`, persisted master and
replicaset name is shown in vshard.router.info:

```
tarantool> vshard.router.info()
---
- replicasets:
    replicaset_1:
      replica: &0
        network_timeout: 0.5
        status: available
        uri: storage@127.0.0.1:3303
        name: replica_1_a
      name: replicaset_1
      master: *0
```

It's needed to check, whether the error was a timeout or not in the
following commit. Let's move this function from vtest to error module.

Needed for tarantool#426

NO_DOC=internal