adjusted runtest.py code to new test data structure

I suspect a recent commit in https://github.com/ethereum/tests/blob/master/trietest.txt broke runtest.py

This pull request fixes a part of the problem and the first two triedata test loops pass with the following test data change: http://paste.ubuntu.com/6878713/

Another problem occurs in subsequent tests -- will report in a separate issue.

Why is the test data kept is a separate repository BTW? Is it reused across multiple repos?
If so, I'd recommend to turn it into a sub-module that allows for a finer revision control and prevents breakage when the test data is modified but the repos that use it have not been updated.