bootstrap: Migrate linguas.sh into bootstrap.conf

bootstrap: Migrate linguas.sh into bootstrap.conf

Bootstrap has infrastructure for downloading/updating project po files
and generating the LINGUAS file. It uses wget instead of rsync, but
provides the same functionality, namely that only po files that have
a modification date before the corresponding one on the server will get
redownloaded. Bootstrap creates a pristine copy of the po files in
po/.reference, so update .gitignore to ignore that directory.

Bootstrap also creates the po/LINGUAS file, but it does not know to add
in GRUB's autogenerated po files. So move that code from linguas.sh into
the bootstrap epilogue.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>