Skip unreadable variables, but don't exit when we do so.

Skip unreadable variables, but don't exit when we do so.

Old versions of efibootmgr and libefivar0 allowed the installation of
necessary EFI boot entries on the affected systems. It seems that an old
libefivar0 did not report read errors.

Then libefivar0 started to crash on unreadable variables (see Debian bug
764386). Since that bug has been fixed, efibootmgr doesn't crash
anymore, but the read errors are reported and efibootmgr always fails
with an input/output error.

Resolves: debian bug 768880

Signed-off-by: Jan Echternach <jan@goneko.de>
Signed-off-by: Daniel Jared Dominguez <Jared_Dominguez@Dell.com>
Signed-off-by: Peter Jones <pjones@redhat.com>