doc: prefix journalctl examples with sudo
doc: prefix journalctl examples with sudo

In a devstack environment you likely need to use sudo
to run the journalctl command, so this adds that to
the examples.

Change-Id: Ibe6b71285a3014e80e06a50130f18bfbdb4ff3ab

group-policy/devstack,nawawi/openstack,noironetworks/devstack,dtroyer/devstack,group-policy/devstack,noironetworks/devstack,dtroyer/devstack,openstack-dev/devstack,openstack-dev/devstack,nawawi/openstack