Show the license warning upon startup if MN not licensed

This changes verifies at the CLI startup the current license
status, and if the valid flag is false, it displays a warning
message to the user with the license status message.

This patch also fixes a minor inconsisteny in the naming
of the license status object type: license_status > license-status

Ref: MN-2498

Signed-off-by: Alex Bikfalvi <alex.bikfalvi@midokura.com>