Avoid double-newlines in salt-call output

When using the salt provisioner with verbose=true, most lines read with an extra newline:
```
[INFO    ] Syncing modules for environment 'base'

[INFO    ] Loading cache from salt://_modules, for base)

```

because the line read has a newline, and emitting the log entry again includes an additional newline.
I can't see how trailing whitespace would be useful.  But honestly I used rstrip because the other parts of this very same file do.  Maybe you should make another branch to change them all if you feel strongly about it.