server:run command: provide more error information

The server:run command didn't provide many information when the executed command exited unexpectedly. Now, the process' exit code is passed through and an error message is displayed.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

This is, for example, useful, if you provide an invalid ip address/hostname on which the server couldn't listen.
I think catching Ctrl+C in this context is not really necessary since the server is stopped in this way. Of course, you could handle the signal and ask the user to confirm the termination. But that's not really convenient in most situations I guess.