Kaiser continues when it can't bind to host's ports

[thoiberg]

When a different docker environment is running and is bound to the same ports that Kaiser is trying to use when it starts, it logs a message and fails to bind the ports for that particular container. However, it then continues with the rest of the setup. This can result in confusing error messages as later steps in the process are assuming that the container was bound successfully.

A possible improvement for this would be for kaiser to fail if the container cannot be bound, and notify the user that the required port is in use and that they need to stop whatever is using that port and retry kaiser again.

Example of how kaiser handles attempting to bind to a port already in use. The error message doesn't really stand out and can easily get buried in the rest of the output text:

docker: Error response from daemon: driver failed programming external connectivity on endpoint nginx (f561316244b4db5830ff146df9b50b25b444ed7aff158081595e895663ec0476): Bind for 0.0.0.0:443 failed: port is already allocated.

# continues on with the rest of the process...

How to replicate

1. Start a separate docker container and bind it to the same port as one that Kaiser will try to use
2. start Kaiser
3. Note a similar error message as the one above and that kaiser continues with the rest of the process