Client does not halt after "contract balance is too low to pay" error

[yaronvel]

I think it should stop.
In any case, please make sure it stops at least for other errors.

[tranvictor]

Introduce hot stop mode, SmartPool will exit immediately whenever it receives error returned by the Contract.
For kovan, we enable hot stop mode by default. The command line also has "--no-hot-stop" param to disable this mode.

Usage:
./smartpool --keystore . --no-hot-stop