improve test output

[MartinNowak]

• properly catch errors and log where they happened
• reduce verbosity a bit
• use common error flags across scripts

[dlang-bot]

Thanks for your pull request, @MartinNowak!

[CyberShadow]

Thanks!!!

[MartinNowak]

Finally manage to get this green, lots of dub search dub failures.
Wondering whether Travis-CI (hosted on Google Cloud) has any particular connectivity issues.
Can't reproduce a single failure with with ab, curl, or dub.

[MartinNowak]

Major improvement btw.

Hope we didn't accidentally mute any tests ;).

Might be interesting to capture verbose dub logs to show them on failure. But atm. it's all easily traced down to failed dub-registry requests.