If the location was invalid, it would write an error response but then
continue to attempt to make the bucket. Whether or not it would succeed,
it would attempt to call response.WriteHeaders twice in a row, which
would cause a message to be logged to the server console (bad).
Here is the relevant Go code:
c80e0d374b/src/net/http/server.go (L878-L881)
Current master has a regression 'mc policy <policy-type> alias/bucket/prefix'
does not work anymore, due to the way new minio-go changes do json marshalling.
This led to a regression on server side when a ``prefix`` is provided
policy is rejected as malformed from th server which is not the case with
AWS S3.
This patch uses the new ``minio-go/pkg/set`` package to address the
unmarshalling problems.
Fixes#2503