cache: decrease log level if cache is not enabled

There is no need to print error messages about cache is disabled
for lookup commands
client: Fixed read_latest policy

If there are no positive lookup result just complete request
with -ENOENT error
tests: Fixed compilation error

Remotes-only version uses nodes_data->directory which accidently
was disabled by #ifdef
Merge pull request #369 from euroelessar/master

Several fixes in cache and client (master)