plugins: correctly output build version, cosmetic cleanups

Now that libcni has the ability to print a version message, plumb it
through correctly.

While we're at it,
- fix import paths
- run gofmt
- add some more comments to sample
- add container runtime swappability for release

plugins/meta/firewall/firewall.go

@@ -26,7 +26,9 @@ import (
 	"github.com/containernetworking/cni/pkg/types"
 	"github.com/containernetworking/cni/pkg/types/current"
 	"github.com/containernetworking/cni/pkg/version"
+
 	"github.com/containernetworking/plugins/pkg/ns"
+	bv "github.com/containernetworking/plugins/pkg/utils/buildversion"
 )
 
 // FirewallNetConf represents the firewall configuration.
@@ -155,7 +157,7 @@ func cmdDel(args *skel.CmdArgs) error {
 }
 
 func main() {
-	skel.PluginMain(cmdAdd, cmdCheck, cmdDel, version.PluginSupports("0.4.0"), "TODO")
+	skel.PluginMain(cmdAdd, cmdCheck, cmdDel, version.PluginSupports("0.4.0"), bv.BuildString("firewall"))
 }
 
 func cmdCheck(args *skel.CmdArgs) error {