fix for docs generation without petsc4py
fix for docs generation without petsc4py

lokik/sfepy,sfepy/sfepy,RexFuzzle/sfepy,RexFuzzle/sfepy,BubuLK/sfepy,vlukes/sfepy,sfepy/sfepy,lokik/sfepy,BubuLK/sfepy,RexFuzzle/sfepy,sfepy/sfepy,lokik/sfepy,lokik/sfepy,vlukes/sfepy,vlukes/sfepy,rc/sfepy,rc/sfepy,rc/sfepy,RexFuzzle/sfepy,BubuLK/sfepy