Fix deploy errors when service isn't running

After a `deploy:stop`, running `deploy` task resulted in following errors

```
*** [err :: qa.poky.huddler.com] /var/www/poky/releases/20130606043610/scripts/poky.init.sh: line 45: kill: (30972) - No such process
```
```
*** [err :: qa.poky.huddler.com] /var/www/poky/releases/20130606050406/scripts/varnish.init.sh: line 53: kill: (31023) - No such process
```

This adds checks to not exit w/ non-zero status when poky/varnish process isn't running