Start building wheels in the mirror

The mirror should build wheels, because they're awesome. However, because
the wheel format does not do fine-grained enough selection on
things like the high likelihood that Ubuntu precise and Ubuntu raring
might have different underlying C libraries for python 2.7, we need to
put our built wheels into a structure that allows them to be used
safely.

lsb_release -r -i is used because Centos lists lsb_release -c as "Final"
which is not particularly helpful. This will wind up with identifying
strings like Ubuntu-12.04 and Centos-6.4 - which should be good enough
for what we need. A call to a shell is used so that the same logic can
be easily duplicated in select-mirror, which is shell, to produce the
appropriate pip.conf file.

Change-Id: Icf360c921dbc357dbeb43386c6e8f51bd5f993ff