Change the default logLevel to ERROR, upgrade some client warnings.

Client side logs are less spammy than server side in general, so more
messages should be visible at the default logLevel when running as a
client.

Server side logging will be spammy basically no matter what unless
obfs4proxy gets into the (arguably dangerous) business of figuring out
which errors are people being evil vs which ones are transient network
issues, so most logging is suppressed by default, unless the admin
choses to open the floodgates.