ofs: add some logging
ofs: add some logging

Previously we had one printf. Now we have key error paths populated
with proper logging statements.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@docker.com>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit,samoht/vpnkit