dracut.sh: add default path for --uefi

dracut.sh: add default path for --uefi

The default output filename for --uefi is
<EFI>/EFI/Linux/linux-$kernel$-<MACHINE_ID>-<BUILD_ID>.efi.
<EFI> might be /efi, /boot or /boot/efi depending on where the ESP partition
is mounted. The <BUILD_ID> is taken from BUILD_ID in /usr/lib/os-release or
if it exists /etc/os-release and is left out, if BUILD_ID is non-existant or
empty.

Also a new option --no-machineid was added, which affects the default output
filename of --uefi and will discard the <MACHINE_ID> part.