Monitor: pull command mapping out of _allowed_command()

We want to be able to validate commands against both the leader and
local command sets, so make that functionality generic.

Signed-off-by: Greg Farnum <greg@inktank.com>
(cherry picked from commit f932903646b4549fe7c2f519a18518c6c81f3ef9)
mon: Monitor: make sure received command is valid before handling it

Fixes: 7611

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
ceph.in: do not allow using 'tell' with interactive mode

This avoids a lot of hassle when dealing with to whom tell each command
on interactive mode, and even more so if multiple targets are specified.

As so, 'tell' commands should be used while on interactive mode instead.

Backport: dumpling,emperor

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
(cherry picked from commit e39c213c1d230271d23b74086664c2082caecdb9)