Explicitly load the config at confd startup

Currently, confd main function doesn't load the config, but simply
forks the individual timer threads, which will—as a side effect-also
load the configuration as soon as they start.

However, this makes codes to the startup more complex, so let's
explicitly (try to) load the configuration as first thing.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>