Docker exceptions are very nondescript since v0.6.0

[vilhelmprytz]

Is your feature request related to a problem? Please describe.
If something goes wrong when Wilfred tries to create a new server (e.g. create the Docker container) and something goes wrong, Wilfred will exit with a very nondescript exception message since v0.6.0. This makes it hard to debug what caused the issue.

Describe the solution you'd like
By default, Wilfred should be a little bit more specific when it comes to printing what went wrong. Then I'd also like to have a verbose argument (-v) and Wilfred can just do the normal Python traceback.

Describe alternatives you've considered
None.

Additional context
This issue was introduced in v0.6.0. Prior versions handle exceptions differently.