authvar: don't exit if no value for CLEAR

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>
authvar: mark "import" as unimplemented

Will do it later...

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>
authvar: check the export file

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>
efisiglist: adjust the signature size

I forgot the size of the owner GUID.

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>