Fix solution printing when problem is unsolvable (#25)

This is a followup from #21

Author: fmassa

autoparallel/optimize_sharding.py

@@ -410,7 +410,7 @@ def get_solution(self, verbose=False):
         self.res = [k for k, v in sol.items() if v == 1]
 
         if self.prob.status == -1:
-            self.print()
+            print(self.get_log())
             raise RuntimeError("Unsolvable problem")
 
         opt = {}