Update item_profile.py

Adds <<inherit>> to the virt-type dropdown box when editing a system or a profile in cobbler_web
Update item_system.py

Adds <<inherit>> to the virt-type dropdown box when editing a system or a profile in cobbler_web
Merge pull request #1172 from jmaas/master

Move all unittests into ./tests/, adjust Makefile accordingly.
Merge pull request #1160 from langimike/master

Add <<inherit>> option to virt-type fields when editing a system or profile in cobbler_web
Remove mention of avahi from the cobbler manual page.