Adding capability to set bootloader filename by profile

[MS-Daniel-Matolcsi]

Currently it is missing from aii-dhcp plugin to fetch bootloader filename for DHCP config.

This issue was raised by the gap of VMware ESXi UEFI bootloader, which is capable only to boot the hypervisor, while there might be occasion (during a rescue mode boot), when there's a need for LiveCD boot. That's not doable with the factory bootloader, hence it has to be handled in the DHCP config to use different bootloaders in specific cases.

Solution would be to make AII capable to add 'filename' option to DHCP config by Quattor profile, also handling normal/rescue mode separately.