Issue172 validate experiment setup

[Mathadon]

@mwetter these changes concatenate (nearly) all error messages into one string. For some error messages I wasn't sure whether they may lead to an except further down the tests so there I did not integrate them.

For a test of this code on a repo where errors are found, see https://travis-ci.org/open-ideas/IDEAS/jobs/382701530 For a test of this code on a repo where no errors are found, see https://travis-ci.org/ibpsa/modelica-ibpsa/jobs/382734297