HEAD-1511 upgrade: CN agent check & agent install needs to handle unavailable or unsetup CNs
HEAD-1511 upgrade: CN agent check & agent install needs to handle unavailable or unsetup CNs

kaizengarden/sdc-headnode,joyent/sdc-headnode,numericillustration/sdc-headnode,joyent/sdc-headnode,joyent/sdc-headnode,joyent/sdc-headnode,kaizengarden/sdc-headnode,numericillustration/sdc-headnode,kaizengarden/sdc-headnode,numericillustration/sdc-headnode,kaizengarden/sdc-headnode