openstack: add PAN_COORDINATOR, COORDINATOR, LEAF roles

[fjmolinas]

This PR want to add a distinction between CORRDINATOR's and LEAF(nodes that can't route). These nodes will node send EB's or DIO.

I changed the terminology from DAGRoot to PAN_COORDINATOR since the routing mechanism "could" be different than RPL (AFAIK).

Integration with openvisualizer would need some changes, although it works as is.

Let me know if this is of interest @changtengfei @TimothyClaeys.

I tested that current functionality still works (as you can see I had to set root twice to switch from COORDINADTOR -> LEAF -> PAN_COORDINATOR):

18:49:04 SUCCESS Setting mote b5d5 as root
18:49:05 SUCCESS Setting mote b5d5 as root
18:49:05 ERROR b5d5 [IEEE802154E] wrong state 1 in startSlot, at slotOffset 1
18:49:06 INFO registering DAGroot 00-12-4b-00-14-b5-b5-d5
18:49:24 SUCCESS b5af [IEEE802154E] synchronized at slotOffset 0
18:49:50 INFO b5af [SIXTOP] sending a 6top request
18:49:52 SUCCESS b5af [SIXTOP] sixtop return code RC_SUCCESS at sixtop state WAIT_ADDRESPONSE
18:52:00 INFO received RPL DAO from bbbb:0:0:0:12:4b00:14b5:b5af
        - parents:
           bbbb:0:0:0:12:4b00:14b5:b5d5
        - children:
18:54:13 INFO received RPL DAO from bbbb:0:0:0:12:4b00:14b5:b5af
        - parents:
           bbbb:0:0:0:12:4b00:14b5:b5d5
        - children:
18:54:53 INFO received RPL DAO from bbbb:0:0:0:12:4b00:14b5:b5af
        - parents:
           bbbb:0:0:0:12:4b00:14b5:b5d5
        - children:
18:56:04 INFO received RPL DAO from bbbb:0:0:0:12:4b00:14b5:b5af
        - parents:
           bbbb:0:0:0:12:4b00:14b5:b5d5
        - children: