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

According to the `rpmUtils.arch` source code, when [no argument](http://yum.baseurl.org/gitweb?p=yum.git;a=blob;f=rpmUtils/arch.py;h=72cba605ce8af2a72ebe624175e9914cf03e430a;hb=30c993c19b8b85f44e7cec436484862ab55a6961#l353) is passed to `rpmUtils.arch.getBaseArch()`, the result should be the same as `rpmUtils.arch.getCanonArch()`[[look here](http://yum.baseurl.org/gitweb?p=yum.git;a=blob;f=rpmUtils/arch.py;h=72cba605ce8af2a72ebe624175e9914cf03e430a;hb=30c993c19b8b85f44e7cec436484862ab55a6961#l320)]. However, in CentOS 6.4 with yum-3.2.29-40.el6.centos.noarch:

```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.

@terminalmage, I need your input on this. Is this the right approach?