Verify if healing and replacing a drive works

```
λ make verify-healing
```

At this point in time the backport is ready to be submitted as a pull request to the relevant branch. A pull request is recommended to ensure [mint](http://github.com/minio/mint) tests are validated. Pull request also ensures code-reviews for the backports in case of any unforeseen regressions.

### Building a hotfix binary and container

[Prometheus](https://prometheus.io) is a cloud-native monitoring platform. Prometheus offers a multi-dimensional data model with time series data identified by metric name and key/value pairs. The data collection happens via a pull model over HTTP/HTTPS. Users looking to monitor their MinIO instances can point Prometheus configuration to scrape data from following endpoints. 

## Community Contribution License
All community contributions in this pull request are licensed to the project maintainers
under the terms of the [Apache 2 license](https://www.apache.org/licenses/LICENSE-2.0). 
By creating this pull request I represent that I have the right to license the 
contributions to the project maintainers under the Apache 2 license.

## Description


## Motivation and Context


## How to test this PR?

| `minio_cluster_erasure_set_write_quorum`         | `gauge` | Write quorum for the erasure set in a pool                    | `pool_id,set_id` |
| `minio_cluster_erasure_set_online_drives_count`  | `gauge` | Count of online drives in the erasure set in a pool           | `pool_id,set_id` |

Push your locally committed changes to the remote origin (your fork)

```
git push origin my-new-feature
```

### Create a Pull Request

Pull requests can be created via GitHub. Refer to [this document](https://help.github.com/articles/creating-a-pull-request/) for detailed steps on how to create a pull request. After a Pull Request gets peer reviewed and approved, it will be merged.

## FAQs

### How does ``MinIO`` manage dependencies?

```

### Things to know

- Fields such as `version` and `pools` are mandatory, however all other fields are optional.
- Each pool expects a minimum of 2 nodes per pool, and unique non-repeating hosts for each argument.
- Each pool expects each host in this pool has the same number of drives specified as any other host.

```
λ mc admin decommission status alias/ http://minio{1...2}/data{1...4}
Decommission of pool http://minio{1...2}/data{1...4} is complete, you may now remove it from server command line
```

### A pool not under decommissioning will throw an error

```
λ mc admin decommission status alias/ http://minio{1...2}/data{1...4}
ERROR: This pool is not scheduled for decommissioning currently.
```

## Canceling a decommission

    for: 5m
    labels:
      severity: critical
    annotations:
      summary: "Instance {{ $labels.server }} has lost quorum on pool {{ $labels.pool }} on set {{ $labels.set }}"
      description: "MinIO instance {{ $labels.server }} of job {{ $labels.job }} has lost quorum on pool {{ $labels.pool }} on set {{ $labels.set }} for more than 5 minutes."
```

## Verify the configuration and alerts

> Notice the requirement of common SLA here original cluster had 1024 drives with 16 drives per erasure set with default parity of '4', second pool is expected to have a minimum of 8 drives per erasure set to match the original cluster SLA (parity count) of '4'. '12' drives stripe per erasure set in the second pool satisfies the original pool's parity count.

> **NOTE:** **Each pool you add must have the same erasure coding parity configuration as the original pool, so the same data redundancy SLA is maintained.**