Add python-catkin_pkg to python.yaml

The package is now available for installation using yum.

```
[asinha@localhost  ~]$ sudo yum info python-catkin_pkg
[sudo] password for asinha:
Loaded plugins: fastestmirror, langpacks, refresh-packagekit, remove-with-leaves
Loading mirror speeds from cached hostfile
 * fedora: fedora.mirror.uber.com.au
 * livna: rpm.livna.org
 * rpmfusion-free: ucmirror.canterbury.ac.nz
 * rpmfusion-free-updates: ucmirror.canterbury.ac.nz
 * rpmfusion-nonfree: ucmirror.canterbury.ac.nz
 * rpmfusion-nonfree-updates: ucmirror.canterbury.ac.nz
 * updates: fedora.mirror.uber.com.au
 * updates-testing: fedora.mirror.uber.com.au
Installed Packages
Name        : python-catkin_pkg
Arch        : noarch
Version     : 0.1.18
Release     : 1.fc19
Size        : 253 k
Repo        : installed
From repo   : updates-testing
Summary     : Library for retrieving information about catkin packages
URL         : https://github.com/ros-infrastructure/catkin_pkg
Licence     : BSD
Description : Library for retrieving information about catkin packages

[asinha@localhost  ~]$
```