update set_conf_solvers(): allow to switch off a solver (e.g. ts in homogenization)
update set_conf_solvers(): allow to switch off a solver (e.g. ts in homogenization)

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