candlepin-common rpm

So we have an initial cut at building the candlepin-common rpm in brew. The Fedora build does not yet work because we have some packages to build in Fedora or we'll have to resurrect candlepin-deps. I'm trying to avoid doing that. For now, let's focus the review on the brew portion.

TEST
------
* Build a a SRPM using tito
```tito build --test --srpm```
* Do a scratch build in brew
```brew build --scratch candlepin-1-rhel-6-candidate /path/to/candlepin-common-SRPM```


> ant-nodeps is required for the symlink taskdef in RHEL 6. I just tried doing a build without it and it fails.

I don't think it's in RHEL 7 though.  I didn't see it in our buildroot at least and in candlepin.spec that requires is under the else section of a `%if 0%{?rhel} >= 7`

I'm thinking maybe we could consolidate and do something like

```
%if 0%{?rhel} < 7
BuildRequires: ant-nodeps >= 0:1.7.0
%else
BuildRequires: ant >= 0:1.7.0
%end
```
Probably should make that change in candlepin.spec too.