cmds/exp/netbootxyz: Refactored netbootxyz.go
cmds/exp/netbootxyz: Refactored netbootxyz.go

Now paring from yaml files work. In addition. netbootxyz will now adjust
entries if Kernel+Initrd are not in the same Filesystem entry.

Whats missing:
* Sub Menus - Only show OS on top, then versions + flavor
* Automatically adjust command line based on OS + Flavor
* Verify all installations

Signed-off-by: Christian Walter <0e8e2a4841637ccc9693af3755dea51f6c46a0f8@9elements.com>

u-root/u-root,u-root/u-root,u-root/u-root