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/range_set.go

@@ -61,7 +61,7 @@ func (s *RangeSet) Canonicalize() error {
 	}
 
 	fam := 0
-	for i, _ := range *s {
+	for i := range *s {
 		if err := (*s)[i].Canonicalize(); err != nil {
 			return err
 		}