Don't restart the ddev-router all the time, fixes #1236

[rfay]

The Problem/Issue/Bug:

OP #1236 - We stop the router and check for potential port conflicts with every single ddev start, and it takes a few seconds in the start. It's unnecessary.

How this PR Solves The Problem:

• Calculate required ports to check for conflicts and only check new ports.
• Just let docker-compose up do the job of deciding whether to recreate ddev-router.

Manual Testing Instructions:

Use a few projects with different ports.
Use ddev start on them and monitor ddev-router behavior.

You can force the occupy-port test with the nc tool, like nc -l 8080 to force occupation of port 8080 to see if the port check does the right thing on ddev start.

Automated Testing Overview:

TestGetExposedContainerPorts() was added for the new GetExposedContainerPorts() utility.
Our existing tests should do the job of testing port overrides and such, as the behavior mostly stays on parallel.

Related Issue Link(s):

OP #1236

[andrewfrench]

I was able to test this on Windows 10 Pro and MacOS.

When re-using ports, new projects are started with ddev-router is up-to-date.

When a project is configured to use a previously unused port, the router is restarted when the project is started.

When a port is already in use (nc -l 8080, ddev config --http-port 8080) and the project is started, the command fails with Unable to listen on required ports, port 8080 is already in use.