Bump default Riak CS version to 1.4.5

Changes:

- Riak `1.4.8` is now the default.
- Riak CS `1.4.5` is now the default.
- Version constraint of `< 3.0` for the `yum` cookbook has been lifted.

Tests:

- [x] Test open source Riak CS install
- [x] Test Riak CS Enterprise install