fix bug 1055268 - Package Socorro

Adds the ability to package an *rpm* of Socorro while not disrupting *tarball* creation.

This can be done in bash by
```bash
$ export BUILD_TYPE=rpm
$ socorro/scripts/build.sh
```

There is also a `make` target for package, but like the install target, it will not work without first exporting environment variables.
Changing the ```install``` target in this way will break the "production install from source" doc, please fix it if you intend to change this:

https://github.com/mozilla/socorro/blob/master/docs/installation/install-src-prod.rst

I would suggest simply removing ```install``` and replacing with ```package```, and update those docs.