Add installation source option snippets (cdrom, harddrive, install, liveimg, nfs, ostreesetup)

[sfloess]

Part of #15: Include all option snippets as found in the kickstart guide.

Scope

Add option snippets for installation source/method kickstart commands. Currently only url exists. The following are missing:

• cdrom - Install from the first optical drive on the system
• harddrive - Install from a local drive (harddrive --partition= --dir=)
• install - Begin an installation (default mode, used to specify source type)
• liveimg - Install from a disk image (live image) instead of packages
• nfs - Install from an NFS server (nfs --server= --dir= [--opts=])
• ostreesetup - Set up OStree-based installations

Reference

RHEL 7 Kickstart Syntax Reference - Section 27.3

Acceptance Criteria

• Each command has a corresponding snippet file under snippets/options/
• Snippets follow the existing pattern/style used by other option snippets in the repo
• Key options for each command are parameterized via cobbler variables