Display more helpful failure information in Commands API

[joshlemer]

As it is, when a Commands api property fails, there isn't a lot of information given as to why it failed, what caused it to fail. For example:

! immutable.Set builder implementations.BitSet builder stateful testing: Fa
  lsified after 9 passed tests.
> Labels of failing property: 
initialstate = Set()
seqcmds = (Result => BitSet(); SizeHint(7375); AddOne(8269); AddAll(List(50
  26)); Result => BitSet(5026, 8269); SizeHint(3490); SizeHint(8271); AddAl
  l(List(6727, 6805)); AddOne(2544))
> ARG_0: Actions(Set(),List(Result, SizeHint(7375), AddOne(8269), AddAll(Li
  st(5026)), Result, SizeHint(3490), SizeHint(8271), AddAll(List(6727, 6805
  )), AddOne(2544)),List())
Found 1 failing properties.

It is nice that it gives the sequence of commands issues, but it would be really great to have info of what actually has broken.

It would be nice to display the following:

• The expected State
• The actual state
• What the Sut was

[jonaskoelker]

I saw the same shortcoming you did and took matters into my own hands: #634. It's not exactly what you suggested, but it's pretty close I think.