fix tests failure if yanc plugin is unavailable
remove bash requirement for test script

This gets a bit convoluted because PIPESTATUS is bash specific
but then bash fails on the POSIX version with a bad fd error.
So in case sh actually links to bash, both types are included.

fixes: #72
Merge pull request #75 from nyov/nyov/runtests-fix

Fix for run-tests.sh where it would fail if nosetests is missing yanc plugin