Also improve healthcheck.
When conf.d does not define an `$address`, curl will try to query a file
(`/minio/health/ready`), which obviously will always fail.
By default, minio will listen on 0.0.0.0:9000, so default to localhost.
Closes: GH-8911
Minio will crash on startup if networking is not available.
A short period of the network dropping should not prevent the service
from coming up once networking is back.
As such, allow infinite respawns.
To avoid CPU thrashing, enforce a 5-second delay between respawns.
