Test: Provide more useful information when unit translation fails

Add the input quantity and the target scheme to the exception output.
Also make the output formatting more canonical and remove the unused
"s" temporary.

src/Mod/Test/UnitTests.py

@@ -121,14 +121,13 @@ class UnitBasicCases(unittest.TestCase):
             q1 = FreeCAD.Units.Quantity(q1)
             q1.Format = {'Precision': 16}
             for idx, val in enumerate(schemes):
-                t = FreeCAD.Units.schemaTranslate(q1, idx)
+                [t, amountPerUnit, unit] = FreeCAD.Units.schemaTranslate(q1, idx)
                 try:
-                    q2 = FreeCAD.Units.Quantity(t[0])
+                    q2 = FreeCAD.Units.Quantity(t)
                     if math.fabs(q1.Value - q2.Value) > 0.01:
                         print (" {} : {} : {} : {} : {}".format(q1, q2, t, i, val).encode("utf-8").strip())
                 except Exception as e:
-                    s = "{}: {}".format(e, t[0])
-                    print (" ".join(str(e)).encode("utf-8").strip())
+                    print ("{} : {} : {} : {}".format(q1, i, val, e).encode("utf-8").strip())
 
     def testVoltage(self):
         q1 = FreeCAD.Units.Quantity("1e20 V")