Fix bad regex in the ecobackend, and raise better error messages

We use regexen to match failures from the ecoservice with their root cause

This regex was failing to match NMtnPrFNL, because it started with two
capital letters.

I've also changed the error parsing to raise a human readable error instead
of the rather cryptic message we get from HTTPError
If only we were using Python 3, we could raise our own exception *and* keep the traceback.
.... sigh