mon: Monitor: sanitize options at start

Make sure some options have sane values.

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
mon: Monitor: observe conf changes and report on unsage option values

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
common: LogClient: output to derr (i.e., dout(-1)) on CLOG_ERROR

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>