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/ipam/dhcp/options_test.go

@@ -24,14 +24,14 @@ import (
 
 func validateRoutes(t *testing.T, routes []*types.Route) {
 	expected := []*types.Route{
-		&types.Route{
+		{
 			Dst: net.IPNet{
 				IP:   net.IPv4(10, 0, 0, 0),
 				Mask: net.CIDRMask(8, 32),
 			},
 			GW: net.IPv4(10, 1, 2, 3),
 		},
-		&types.Route{
+		{
 			Dst: net.IPNet{
 				IP:   net.IPv4(192, 168, 1, 0),
 				Mask: net.CIDRMask(24, 32),