freeport is a copy of the freeport package found in
github.com/hashicorp/consul/sdk/freeport with modifications to remove
dependencies on other consul/sdk packages.
Take returns a list of free ports from the allocated port block. It is safe
to call this method concurrently. Ports have been tested to be available on
127.0.0.1 TCP but there is no guarantee that they will remain free in the
future.