move from '/usr/bin/nosetests' to more general '$(which nosetests)'
move from '/usr/bin/nosetests' to more general '$(which nosetests)'


Former-commit-id: e0f61c25e11f1bef08d4ffa5b2a2ad7a94781c85
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine