When creating the successor, the current active key (predecessor)
should change its goal state to HIDDEN.
Also add two useful debug logs in the keymgr_key_rollover function.
(cherry picked from commit e71d60299f)
The logic in `keymgr_key_has_successor(key, keyring)` is flawed, it
returns true if there is any key in the keyring that has a successor,
while what we really want here is to make sure that the given key
has a successor in the given keyring.
Rather than relying on `keymgr_key_exists_with_state`, walk the
list of keys in the keyring and check if the key is a successor of
the given predecessor key.
(cherry picked from commit 0d578097ef)
