Get rid of chatter for failed commands if the filesystem is read-only.
Include /var/db/entropy-file in the reseeding if present. It is used for
last-ditch efforts to save entropy and thus should also be used to seed
the RNG when starting. Print a warning instead of an error if writing the
file fails -- err() exits, preventing the umask from being restored.
Also, since there's not much that can be done about it, notifying the user
is all that's needed.

MFC after: 2 weeks