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/host-local/backend/allocator/config_test.go

@@ -45,7 +45,7 @@ var _ = Describe("IPAM config", func() {
 			Name: "mynet",
 			Type: "host-local",
 			Ranges: []RangeSet{
-				RangeSet{
+				{
 					{
 						RangeStart: net.IP{10, 1, 2, 9},
 						RangeEnd:   net.IP{10, 1, 2, 20},