Replace `rpmUtils.arch.getBaseArch()` with `rpmUtils.arch.getCanonArch()`.

According to the `rpmUtils.arch` source code, when no argument is passed to `rpmUtils.arch.getBaseArch()`, the result should be the same as `rpmUtils.arch.getCanonArch()`. However, in CentOS 6.4 with the XXX version of `yum`:

```python
>>> import rpmUtils.arch
>>> rpmUtils.arch.getBaseArch()
'i386'
>>> rpmUtils.arch.getBaseArch(None)
'i386'
>>> rpmUtils.arch.getCanonArch()
'i686'
>>>
```

This little thing made the `pkg.latest` state fail, and also the `pkg.latest_version` module function.