update test_io.py for pytest, clean up
update test_io.py for pytest, clean up

BubuLK/sfepy,vlukes/sfepy,BubuLK/sfepy,sfepy/sfepy,BubuLK/sfepy,sfepy/sfepy,vlukes/sfepy,sfepy/sfepy,rc/sfepy,rc/sfepy,vlukes/sfepy,rc/sfepy