Fix un-failable tests.

Some existing test are using backticks operator and validating the tests on whether there is any output at all but ignoring stderr. By default in rsnapshot error output goes to stderr. Fixed by add `2>&1` to these existing tests. That is:
```
git clone https://github.com/DrHyde/rsnapshotcd rsnapshot
./configure
prove
# all tests should pass.
editor t/support/etc/rsync.conf
# mess it up however you want and save it.
prove
# all tests pass.
```

I'd say in the long run it would be better not to use back ticks but this is the least change - most likely to be accepted change so went with this.