For 'snapshot' type profiles, record a 'before' profile that can be used
as `go tool pprof -base=before ...` to compare before and after.
"Before" profiles are included in the zipped package.
[`runtime.MemProfileRate`](https://golang.org/pkg/runtime/#pkg-variables)
should not be updated while the application is running, so we set it at startup.
Co-authored-by: Harshavardhana <harsha@minio.io>