[PATCH] add all systems options to cobbler buildiso command

[Jörgen Maas]

Hello my fellow cobblers :)

These little patches add the ability to use the "all" keyword for the
"cobbler buildiso --system=" command, also the usage text for this
command has been updated.
I hope the patch format is usable for you guys... (i used diff -u,
will setup a git repo later...)

Have a nice day!

Grtz,
Jorgen Maas