When using hiera-eyaml with a hiera.yaml like:
~~~yaml
---
:backends:
  - eyaml
  - yaml
:eyaml:
  :datadir: '/etc/puppet/code/environments/production/hieradata'
:yaml:
  :datadir: '/etc/puppet/code/environments/production/hieradata'
...
~~~

Octocatalog-diff was rewriting only the yaml (and/or json) datadir
and not other backends datadir.

This changes rewrites all datadir from all declared backends.

Signed-off-by: Brice Figureau <brice@daysofwonder.com>