This also modifies the test to explicitly test each of the equilibrium solvers,
so that failures in any one solver aren't hidden by the fact that a different
solver works for a particular initial condition.
The old version of this test didn't actually check any meaninful results. The
ChemEquil and VCS solvers are both able to solve this problem, but the
MultiPhase solver currently fails. Also, the BasisOptimize function may fail
depending on the order that the elements are specified in the input file.