mon,auth: AuthMonitor, KeyRing: add Formatter-dumps of auth info

mon,auth: AuthMonitor, KeyRing: add Formatter-dumps of auth info

Signed-off-by: Dan Mick <dan.mick@inktank.com>
auth: KeyRing: encode_formatted() receives a label as first argument

Also, this allows us to standardize formatted output on the AuthMonitor,
so that all output starts with a section 'auth'.  Other subsystems using
the KeyRing class, can specify whatever section they prefer.

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