Fixes https://github.com/hashicorp/nomad/issues/5587
When a nomad 0.9 client is handling an alloc generated by a nomad 0.8
server, we should check the alloc.TaskResources for networking details
rather than task.Resources.
We check alloc.TaskResources for networking for other tasks in the task
group [1], so it's a bit odd that we used the task.Resources struct
here. TaskRunner also uses `alloc.TaskResources`[2].
The task.Resources struct in 0.8 was sparsly populated, resulting to
storing of 0 in port mapping env vars:
```
vagrant@nomad-server-01:~$ nomad version
Nomad v0.8.7 (21a2d93eecf018ad2209a5eab6aae6c359267933+CHANGES)
vagrant@nomad-server-01:~$ nomad server members
Name Address Port Status Leader Protocol Build Datacenter Region
nomad-server-01.global 10.199.0.11 4648 alive true 2 0.8.7 dc1 global
vagrant@nomad-server-01:~$ nomad alloc status -json 5b34649b | jq '.Job.TaskGroups[0].Tasks[0].Resources.Networks'
[
{
"CIDR": "",
"Device": "",
"DynamicPorts": [
{
"Label": "db",
"Value": 0
}
],
"IP": "",
"MBits": 10,
"ReservedPorts": null
}
]
vagrant@nomad-server-01:~$ nomad alloc status -json 5b34649b | jq '.TaskResources'
{
"redis": {
"CPU": 500,
"DiskMB": 0,
"IOPS": 0,
"MemoryMB": 256,
"Networks": [
{
"CIDR": "",
"Device": "eth1",
"DynamicPorts": [
{
"Label": "db",
"Value": 21722
}
],
"IP": "10.199.0.21",
"MBits": 10,
"ReservedPorts": null
}
]
}
}
```
Also, updated the test values to mimic how Nomad 0.8 structs are
represented, and made its result match the non compact values in
`TestEnvironment_AsList`.
[1] 24e9040b18/client/taskenv/env.go (L624-L639)
[2] https://github.com/hashicorp/nomad/blob/master/client/allocrunner/taskrunner/task_runner.go#L287-L303
