Swarm routes traffic only to containers that report healthy status,
while Minio in distributed mode needs to talk to other peers before
it can respond to healthcheck probe. As the Minio containers are not
able to talk to each other, distributed Minio is not getting started
on Docker Swarm.
With this PR, Minio Healthcheck report healthy status for initial
120s enough for distributed Minio to start. After that normal
Healthcheck resumes. Also changed the healthcheck method name
in accordance with Google shell styleguide.
Fixes: https://github.com/minio/minio/issues/4761
