Add capability to set rescue mode bootloader filename

[MS-Daniel-Matolcsi]

This commit adds the feature to aii-dhcp plugin to fetch bootloader filename for DHCP config to be included. Also handles situation if default bootloader may differ from the one would be used in case of rescue mode.

Resolves #343.

[jouvin]

I don't think you need AII to configure anything in DHCP. It is currently support by AII to boot in rescue mode (can in fact be anything you have configured) by executing "aii-shellfe --rescue node.name". To work, you need to write a Grub2 config file rescue.cfg file similar to localboot.cfg that will be used by the node when booting. rescue.cfg can be something like (not sure it is a working configuration):

---

set default=0
set timeout=2
menuentry "Rescue CentOS 7 (x86_64)" {
set root=(pxe)
linuxefi /quattor/rescue-el7_x86_64/vmlinuz ro crashkernel=auto rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb
initrdefi /quattor/rescue-el7_x86_64/initrd.img
}
}

You can also do something similar for legacy BIOS if you need.

Did I miss something in your usecase?

[MS-Daniel-Matolcsi]

We specifically need to use a different bootloader when using rescue mode. This is an edge case ESXi hypervisors' UEFI booting:

• normally using VMware's mboot.efi, but it can't do a chainload or boot a LiveCD image
• hence, in case we have to boot from a Linux LiveCD in case of rescue (eg. due to revise hardware / doing an firmware upgrade), we have to switch to grub-efi eg. That is what covered in my change, if it's given in profile, AII would change 'filename' option in DHCP conf.

[stdweird]

@MS-Daniel-Matolcsi is this the same as #357 ?

[stdweird]

@MS-Daniel-Matolcsi yours is better, but you will also need the https://github.com/quattor/aii/pull/357/files#diff-bf9d1e359bea07dacdbbcf6dab94b9a2f4c42b8a8fde532bf7e96b3f3d71dbf2R11 line for your PR

[stdweird]

#299 also has the filename set option already (and i forgot about it, it's open for soooo long ;)