Add support for kickstart repo parameter

kickstart can be told to look for packages in additional yum repositories by using the repo parameter. Copying from https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/5/html/Installation_Guide/s1-kickstart2-options.html:

repo (optional)

    Configures additional yum repositories that may be used as sources for package installation. Multiple repo lines may be specified.

    repo --name=<repoid> [--baseurl=<url>| --mirrorlist=<url>]

        --name= — The repo id. This option is required.

        --baseurl= — The URL for the repository. The variables that may be used in yum repo config files are not supported here. You may use one of either this option or --mirrorlist, not both.

        --mirrorlist= — The URL pointing at a list of mirrors for the repository. The variables that may be used in yum repo config files are not supported here. You may use one of either this option or --baseurl, not both.