lib/sign: add revoking mechanism for ed25519 keys
lib/sign: add revoking mechanism for ed25519 keys

Skip public keys verification if key is marked as invalid key.
Allow to redefine system-wide directories for ed25519 verification.
Minor bugfixes.

Signed-off-by: Denis Pynkin <3fbf95ee68899518ee8799d35f88c8f7982aa936@collabora.com>

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree