templates: Properly handle multiple initrd paths in 30_os-prober

templates: Properly handle multiple initrd paths in 30_os-prober

os-prober now effectively handles multiple paths passed to initrd, but
grub-mkconfig still truncates off any subsequent space-delimited paths.

Support proper parsing of space-delimited initrd paths passed from
os-prober for distributions, like Manjaro, that require it.

Fixes: https://savannah.gnu.org/bugs/?47681
Signed-off-by: Peter Levine <plevine457@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>