Fix C2S instance bootup

• C2S instances wouldn't boot because of missing network drivers. Thanks to @stoerchl for finding and fixing this issue.
• added kill switch for disabling kexec on bootup via scaleway server tag. Add ubuntukernel_disabled to your tags to disable kexec and remove the tag to enable it again.

Tested on C2S but couldn't test it on VC instances as they were out of stock. Release 1.1 works for sure on VC instances.

IPXE script fix

• fix parsing of Scaleway IPXE script (by github.com/ivan)
• get current kernel by reading /vmlinuz link

initial debian package

Installable Ubuntu package which only required a linux-image.