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.go

@@ -97,7 +97,7 @@ func LoadIPAMConfig(bytes []byte, envArgs string) (*IPAMConfig, string, error) {
 		n.IPAM.IPArgs = append(n.IPAM.IPArgs, n.Args.A.IPs...)
 	}
 
-	for idx, _ := range n.IPAM.IPArgs {
+	for idx := range n.IPAM.IPArgs {
 		if err := canonicalizeIP(&n.IPAM.IPArgs[idx]); err != nil {
 			return nil, "", fmt.Errorf("cannot understand ip: %v", err)
 		}
@@ -122,7 +122,7 @@ func LoadIPAMConfig(bytes []byte, envArgs string) (*IPAMConfig, string, error) {
 	// Validate all ranges
 	numV4 := 0
 	numV6 := 0
-	for i, _ := range n.IPAM.Ranges {
+	for i := range n.IPAM.Ranges {
 		if err := n.IPAM.Ranges[i].Canonicalize(); err != nil {
 			return nil, "", fmt.Errorf("invalid range set %d: %s", i, err)
 		}