cmfm: allow prompt console without su command

Separete shell console commands from su command. This allow to create a shell
console when su command is not present. A warning will be displayed is root
mode is trying to be selected or a elevated operation is required.

Change-Id: I27a2e850aec87026c8dd4b3baacf7ebd0f897a1a
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>