Implement profiling command to start & download profiling data of
a standalone or all nodes of a cluster.
```
1. Start CPU profiling
$ mc admin profiling start --type "cpu" myminio/
2. Download latest profiling data under save under profiling.zip
$ mc admin profiling stop myminio/
```
Additionally this PR also allows for creating
prefixes on S3 compatible object storage backends
in the following form
```
mc mb s3/harshavardhana/object/prefix/
```
The probe package is no longer available in the Minio server
repo. This change just moves probe from the vendor directory to its
own dir under `pkg`.
This is a maintenance fix.
