testutils/iotlab.py: Randomize the selected node

It seems there have been some failures mainly
due to infrastructure. Specifically the samr21-xpro
failing to flash will cause many reruns with the same
faulty hardware.

Previously it would just take the first available
node in the list, which is deterministic but doesn't
help with flakey test reruns. This may cause an issue
with distance to other nodes, but if random selection
of nodes becomes a problem we would have to introduce
node pairing lists... Which is a bit more work.

This is at least a first step.

testutils/iotlab.py

@@ -1,4 +1,5 @@
 import logging
+import random
 import re
 
 from iotlabcli.auth import get_user_credentials
@@ -9,6 +10,7 @@
     stop_experiment,
     get_experiment,
     exp_resources,
+    info_experiment,
     AliasNodes,
 )
 
@@ -151,6 +153,25 @@ def _wait(self):
         ret = wait_experiment(Api(*self.user_credentials()), self.exp_id)
         return ret
 
+    def _select_random_node(self, site, board):
+        api = Api(*self.user_credentials())
+        info = info_experiment(api, site=site)
+        choices = []
+        for iot_lab_nodes in info.values():
+            if not isinstance(iot_lab_nodes, list):
+                continue
+            for iot_lab_node in iot_lab_nodes:
+                if iot_lab_node.get("state", "") != "Alive":
+                    continue
+                net_addr = iot_lab_node.get("network_address", "")
+                if board not in net_addr:
+                    continue
+                choices.append(net_addr)
+        if not choices:
+            raise RuntimeError(f"No {board} found at {site}")
+        ret = random.choice(choices)
+        return ret
+
     def _submit(self, site, duration):
         """Submit an experiment with required nodes"""
         api = Api(*self.user_credentials())
@@ -159,9 +180,19 @@ def _submit(self, site, duration):
             if ctrl.env.get('IOTLAB_NODE') is not None:
                 resources.append(exp_resources([ctrl.env.get('IOTLAB_NODE')]))
             elif ctrl.board() is not None:
-                board = IoTLABExperiment._archi_from_board(ctrl.board())
-                alias = AliasNodes(1, site, board)
-                resources.append(exp_resources(alias))
+                # Since we cannot combine alias and phyical nodes in the same
+                # experiment and but we would prefer to use iotlab-m3 alias
+                # nodes because the m3 nodes can report that they are broken.
+                # Let's take the easiest solution and only use alias nodes
+                # if they are all iotlab-m3 nodes.
+                if all([ctrl.board() == 'iotlab-m3' for ctrl in self.ctrls]):
+                    board = IoTLABExperiment._archi_from_board(ctrl.board())
+                    alias = AliasNodes(1, site, board)
+                    resources.append(exp_resources(alias))
+                else:
+                    board = IoTLABExperiment.BOARD_ARCHI_MAP[ctrl.board()]['name']
+                    net_addr = self._select_random_node(site, board)
+                    resources.append(exp_resources([net_addr]))
             else:
                 raise ValueError("neither BOARD or IOTLAB_NODE are set")
         return submit_experiment(api, self.name, duration, resources)['id']