Improve how Wasp handles and reports unavailable ports

[sodic]

Version: 0.15.2

Steps to reproduce:

• Start a process (not Wasp) that listens on port 3001. For example: python -m http.server 3000
• Execute wasp start.
• Wasp will fail and tell you "Port 3001 is taken" (not 3000).

What happens:

• The client sees port 3000 is taken and automatically falls back to 3001.
• The server sees port 3001 is taken and crashes with the incorrect error.

It's a confusing experience because the client's message that says "Port 3000 is in use, trying another one..." is printed earlier and gets lost in the noise, while the server's message that says "Port 3001 is already in use" is the last (and possibly the only) thing the user sees.

@Martinsos Don't we already have an issue for this? I couldn't find it.