update to scarcity example in test

reflects move of vensim.py to connectors folder
update to vensim.py

vensim.py now creates an array filled with NANs, then the results are
put into this array. If runs don't complete the NANs can be used to
quickly find these runs.

also small change to test code
bug fix in vensim.py
Merge pull request #1 from quaquel/master

test pull