Do not validate snapshotter argument if docker is enabled

Problem:
While using ZFS on debian and K3s with docker, I am unable to get k3s working as the snapshotter value is being validated and the validation fails.

Solution:
We should not validate snapshotter value if we are using docker as it's a no-op in that case.

Signed-off-by: Waqar Ahmed <waqarahmedjoyia@live.com>

pkg/agent/config/config.go

@@ -433,6 +433,7 @@ func get(envInfo *cmds.Agent, proxy proxy.Proxy) (*config.Node, error) {
 	nodeConfig.CACerts = info.CACerts
 	nodeConfig.Containerd.Config = filepath.Join(envInfo.DataDir, "agent", "etc", "containerd", "config.toml")
 	nodeConfig.Containerd.Root = filepath.Join(envInfo.DataDir, "agent", "containerd")
+	if !nodeConfig.Docker && nodeConfig.ContainerRuntimeEndpoint == "" {
 		switch nodeConfig.AgentConfig.Snapshotter {
 		case "overlayfs":
 			if err := overlay.Supported(nodeConfig.Containerd.Root); err != nil {
@@ -445,6 +446,7 @@ func get(envInfo *cmds.Agent, proxy proxy.Proxy) (*config.Node, error) {
 					nodeConfig.Containerd.Root)
 			}
 		}
+	}
 	nodeConfig.Containerd.Opt = filepath.Join(envInfo.DataDir, "agent", "containerd")
 	if !envInfo.Debug {
 		nodeConfig.Containerd.Log = filepath.Join(envInfo.DataDir, "agent", "containerd", "containerd.log")