Split devicemanager Allocate into two functions

Instead of having a single call for Allocate(), we now split this into two
functions Allocate() and UpdatePluginResources().

The semantics split across them:

// Allocate configures and assigns devices to a pod. From the requested
// device resources, Allocate will communicate with the owning device
// plugin to allow setup procedures to take place, and for the device
// plugin to provide runtime settings to use the device (environment
// variables, mount points and device files).
Allocate(pod *v1.Pod) error

// UpdatePluginResources updates node resources based on devices already
// allocated to pods. The node object is provided for the device manager to
// update the node capacity to reflect the currently available devices.
UpdatePluginResources(
    node *schedulernodeinfo.NodeInfo,
    attrs *lifecycle.PodAdmitAttributes) error

As we move to a model in which the TopologyManager is able to ensure
aligned allocations from the CPUManager, devicemanger, and any
other TopologManager HintProviders in the same synchronous loop, we will
need to be able to call Allocate() independently from an
UpdatePluginResources(). This commit makes that possible.

pkg/kubelet/cm/container_manager_linux.go

@@ -672,7 +672,11 @@ func (cm *containerManagerImpl) GetResources(pod *v1.Pod, container *v1.Containe
 }
 
 func (cm *containerManagerImpl) UpdatePluginResources(node *schedulernodeinfo.NodeInfo, attrs *lifecycle.PodAdmitAttributes) error {
-	return cm.deviceManager.Allocate(node, attrs)
+	err := cm.deviceManager.Allocate(attrs.Pod)
+	if err != nil {
+		return err
+	}
+	return cm.deviceManager.UpdatePluginResources(node, attrs)
 }
 
 func (cm *containerManagerImpl) GetTopologyPodAdmitHandler() topologymanager.Manager {