Replace use of access(2) in ocat(1)

[jpmens]

ocat is a setuid program which uses access(2) to verify accessibilty of the defaults file. I don't see how this hasn't surfaced previously, but that is an incorrect use:

The access() system call uses the real user ID in place of the effective user ID, the real group ID in place of the effective group ID, and the rest of the group access list.

I noticed this while tailing logs for #536

ocat: Skipping open defaults file /etc/default/ot-recorder: Permission denied

[jpmens]

fixed in daaf71f