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>