gpo: Decode base64 root cert before importing
The reasoning behind this is described in the previous commit message,
but essentially this should either be wrapped in certificate blocks and
imported as PEM, or converted back to binary and imported as DER.
I've opted for the latter since it's how it used to work before it
regressed in
157335ee93e.
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15557
Signed-off-by: Gabriel Nagy <gabriel.nagy@canonical.com>
Reviewed-by: David Mulder <dmulder@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>