Show better errors when things go wrong

These are two minor changes to add the item that is causing
the problem when an exception is thrown.

I personally ran across eac7d8e when I had a bad rootPOM specified
in my job config.  It took disabling the maven info plugin to figure
out what was going wrong.

I did 39f8e27 just because it might have a similar problem, but I
haven't run across it.