logging: Set remote appender log level to off by default

Unless explicitly configured, we should not attempt to send any log events to
the remote appender (both for performance reasons and as a workaround for the
problem with the socket appender connecting to itself).

Target: trunk
Request: 2.6
Require-book: yes
Require-notes: yes
Patch: http://rb.dcache.org/r/5664/
Acked-by: Albert Rossi <arossi@fnal.gov>