Builddrone: add information about buildstep to the errorlog

[ichthyo]

Currently, the errorlog output (as available via Web) is extremely difficult to understand, because the missing crucial information what build step is logged where. Thus, it's often almost impossible to find out what exactly went wrong.

Thus, we should try to add the following informations:

• a timestamp at the top of the log
• a visible separation between the various tasks
• at top of each task an clear identifier denoting the task
• ideally each task would start with a literal copy of the issued commandline (so it can be reproduced on a local system)

[ct]

already covered in #38, maybe reopen this a sub-ticket for #38, but I guess this is not needed.

[ichthyo]

sorry, I disagree. #38 is geared towards a nice "report" on the web (and additionally is worded as just covering the testsuite), whereas this ticket is meant as an immediate fix for the existing plain-text errorlog. For me, #38 seems to be about creating something new and might require a bit more of additional work, while this here is a simple improvement to the status quo.

I think it's just fine that all of the output of the build and test running steps goes as-is into a plaintext log. Just working with this log as it is today can be a pain; but adding some "echo" statements at the right places will easily resolve this situation. My guess would be, that someone familiar with builddrone might actually resolve this ticket in half an hour. (I'd certainly do it myself, just I don't know right now where to look and how to change things...)