Allow rc.initdiskless to find configuration in subdirectories.

[jonathan]

Summary

The current implementation of rc.initdiskless uses a glob pattern to find
local configuration directories and files, e.g., /conf/192.168.1.1/etc.
This approach has the limitation of only working with a single level of
configuration directory: one cannot use /conf/192.168.1.1/etc/ssh, as that
will be seen as an "/ssh" directory.

This commit uses find(1) instead, which is a little more complex but allows
for more sophisticated diskless setups, e.g., with custom per-host
/etc/ssh/sshd_config files.

[crees]

I was thinking that I prefer something like * */* */*/*, but it is probably no faster and certainly less clear (and off the top of my head it might even break if unmatched?).

This is better.