added optional 'options' parameter to start/stop

I've noticed that some units take longer to stop and it may be useful to be able to pass in ```--no-block``` to the ```stop``` command if we absolutely need to know that the command was successful. Since ```start``` takes the same flags, I added the capability to that as well. 

The ```options``` parameter is optional. All of these examples are valid:

```--no-block``` option:
```
var fleetctl = require('fleetctl');
var Fleetctl = new fleetctl({
	binary: 'fleetctl --endpoint=http://192.168.1.100:4001'
});
Fleetctl.stop(units, "--no-block", function (err) {
       // waiting until the unit(s) stops....
});
```

Multiple options:
```
var fleetctl = require('fleetctl');
var Fleetctl = new fleetctl({
	binary: 'fleetctl --endpoint=http://192.168.1.100:4001'
});
Fleetctl.stop(units, ["--no-block=false", "--block-attempts=50"], function (err) {
       // waiting for units to stop, 50 attempts....
});
```

Default options:
```
var fleetctl = require('fleetctl');
var Fleetctl = new fleetctl({
	binary: 'fleetctl --endpoint=http://192.168.1.100:4001'
});
Fleetctl.stop(units, function (err) {
       // this uses the default options:
       // --block-attempts=10
       // --no-block=false
});
```