This changes as many of the integraton tests as possible so that they
use port forwarding rather than the docker IP directly.
Using the docker IP directly does not work on macOS and Windows as the
docker images are running in a VM rather than a container.
This adds the PORTS.md document to document which port numbers we are
using for which service as they need to be unique.
This is possible now that we no longer support go1.12 and brings
rclone into line with standard practices in the Go world.
This also removes errors.New and errors.Errorf from lib/errors and
prefers the stdlib errors package over lib/errors.
This is implemented as a state machine parser so it can emit sensible
error messages.
It does not use the connection strings elsewhere in rclone yet - see
subsequent commits.
An optional fuzzer is implemented for the Parse function.
Currently if container under test has multiple IP addresses,
the `docker_ip` function from `docker.sh` will return a gibberish.
This patch makes it return the first address found.
Additionally, I apply shellcheck on `docker.sh`.
