core/legal-info: generate a hash of all saved files

core/legal-info: generate a hash of all saved files

Having a hash of the saved files can be interesting for the recipient to
verify the integrity of the files.

We remove the warning file earlier, to exclude it from the hash
list.

We generate the hash list in a temporary file that will not be matched
by the "find" expression, and once the file is generated, we remain it
to its final name.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Luca Ceresoli <luca@lucaceresoli.net>
Acked-by: Luca Ceresoli <luca@lucaceresoli.net>
Tested-by: Luca Ceresoli <luca@lucaceresoli.net>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
[Thomas: adjust indentation, improve commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>