fix piezo_elasticity plots - reduce output to 4 figures
fix piezo_elasticity plots - reduce output to 4 figures

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