Add number of total mutations in progress message

[satvug]

Instead of 'Current test: x', write 'Current test: x/y' so we can easily see how far we are in the test

[coveralls]

Coverage decreased (-0.2%) to 90.336% when pulling da00264 on satvug:patch-2 into c40028d on cisco-sas:next.

[BinyaminSharet]

Thanks.

1. Please replace model._num_mutations with model.num_mutations()
2. Please submit it to the 'next' branch.

[satvug]

@BinyaminSharet - Done :)

[BinyaminSharet]

Thank you :)