mon: mon_osd_down_out interval can prompt osdmap creation when nothing is happening
I saw a cluster where we had the whole gamut of no* flags set in an attempt to stop it creating maps.
Unfortunately, the OSDs were turned off for a while and one way or another it got into the tick() block where it marks OSDs out. Now, it didn't mark any OSDs out because the noout flag was set — but it still set do_propose = true and generated a new osdmap. Injecting mon_osd_down_out = 0 stopped the map generation.