[polisher/fedora] Fetch user packages from pkdb api.

For starters, the previous `PACKAGE_LIST` was not working since pkgdb2 is using new uris, hence the method was broken. Then I thought since there is an [API](https://admin.fedoraproject.org/pkgdb/api/#user%27s_packages), why not use it?

So, `gems_owned_by(user)` now fetches a user's packages, both owned and co-maintained. If you wish to fetch only the ones a packager owns, I can simply remove the second query.

As for the tests, this method had [no tests](https://github.com/ManageIQ/polisher/blob/master/spec/fedora_spec.rb#L10) to begin with, but I'm not so familiar with rspec to test api queries. If anyone can point me how to test this, I'll happily implement it.
I did a quick search before I removed any code and I didn't find any calls to `fedora.rb`.
I searched with the generic word fedora:

**ack fedora lib/**
```                                                                                                                     git:polisher_fedora
lib/polisher/koji.rb
21:      conf_attr :koji_url, 'koji.fedoraproject.org/kojihub'

lib/polisher/git/pkg.rb
28:        conf_attr :dist_git_url, 'git://pkgs.fedoraproject.org/'

lib/polisher/fedora.rb
13:      PACKAGE_LIST_API = 'https://admin.fedoraproject.org/pkgdb/api'
45:          bl.call(:fedora, pkg_name, versions) unless bl.nil?

lib/polisher/version_checker.rb
15:    FEDORA_TARGET = :fedora
18:    BODHI_TARGET  = :bodhi  # fedora dispatches to bodhi so not enabled by default
54:          require 'polisher/fedora'
55:          logger.debug "versions_for<fedora>(#{name})..."
56:          fedora_versions = Fedora.versions_for(name, &bl)
57:          logger.debug fedora_versions
58:          versions.merge! :fedora => fedora_versions
61:          versions.merge! :fedora => unknown_version(:fedora, name, &bl)

lib/polisher/bodhi.rb
7:# https://github.com/fedora-infra/fedora-packages/issues/55
11:  # fedora pkgwat provides a frontend to bodhi

lib/polisher.rb
20:require 'polisher/fedora'
```