mon: add `osd destroy`

mon: add `osd destroy`

This new command will remove a given osd's auth keys, along with any
daemon-private and dm-crypt info contained in the config-key store,
without actually removing the osd from crush.

Instead of removing the osd from the osdmap, we mark it as `destroyed`,
thus preventing competing, racing commands from recreating the osd.

Signed-off-by: Joao Eduardo Luis <joao@suse.de>