support host/CSI volumes and using podman tasks as CSI plugins

[tgross]

Fixes #168.

Tested running a job as both a CSI plugin and with a host volume:

jobspec

job "hostpath" {
  datacenters = ["dc1"]

  group "plugins" {

    volume "host_data" {
      type      = "host"
      read_only = false
      source    = "shared_data"
    }

    task "plugin" {
      driver = "podman"
      config {
        image = "quay.io/k8scsi/hostpathplugin:v1.2.0"
        args = [
          "--drivername=csi-hostpath",
          "--v=5",
          "--endpoint=${CSI_ENDPOINT}",
          "--nodeid=node-${NOMAD_ALLOC_INDEX}",
        ]

        cap_add = ["SYS_ADMIN"]
      }

      csi_plugin {
        id        = "hostpath-plugin0"
        type      = "monolith"
        mount_dir = "/csi"
      }

      volume_mount {
        volume      = "host_data"
        destination = "/host_data"
        read_only   = false
      }

      resources {
        cpu    = 256
        memory = 128
      }
    }
  }
}

Working host volume:

$ nomad alloc exec 8c01 ls /host_data
example.txt

Working CSI plugin:

$ nomad plugin status hostpath
ID                   = hostpath-plugin0
Provider             = csi-hostpath
Version              = v1.2.0-0-g83590990
Controllers Healthy  = 1
Controllers Expected = 1
Nodes Healthy        = 1
Nodes Expected       = 1

Allocations
ID        Node ID   Task Group  Version  Desired  Status   Created  Modified
8c012686  c53f3ea2  plugins     0        run      running  16s ago  4s ago

$ nomad volume create ./hostpath.hcl
Created external volume a395c7f1-d7a8-11ec-bc8c-1eac4d1b7ed8 with ID VOLUME_NAME

$ nomad volume status VOLUME_NAME
ID                   = VOLUME_NAME
Name                 = VOLUME_NAME
External ID          = a395c7f1-d7a8-11ec-bc8c-1eac4d1b7ed8
Plugin ID            = hostpath-plugin0
Provider             = csi-hostpath
Version              = v1.2.0-0-g83590990
Schedulable          = true
Controllers Healthy  = 1
Controllers Expected = 1
Nodes Healthy        = 1
Nodes Expected       = 1
Access Mode          = <none>
Attachment Mode      = <none>
Mount Options        = flags: [REDACTED]
Namespace            = default

Topologies
Topology  Segments
01        topology.hostpath.csi/node=node-0

Allocations
No allocations placed

[lgfa29]

Thanks @tgross 🎉