URL based configuration for git exec timeouts and git submodule cloning

Adds a number of user-accessable options for configuring internal git resource
cloning behavior.
- Git commands are executed with a configurable timeout by including a parameter
  like "?timeout=2m30s" in the resource URL. This can improve cloning a large
  repository, or over a slow network.
- Git submodule cloning can be disabled by including a parameter like
  "?submodules=false" in the resource URL.
- Switch the overall query parsing to use url.Parse() and be more extensible.

api/internal/git/gitrunner.go

@@ -12,9 +12,6 @@ import (
 	"sigs.k8s.io/kustomize/api/internal/utils"
 )
 
-// Arbitrary, but non-infinite, timeout for running commands.
-const defaultDuration = 27 * time.Second
-
 // gitRunner runs the external git binary.
 type gitRunner struct {
 	gitProgram string
@@ -24,7 +21,7 @@ type gitRunner struct {
 
 // newCmdRunner returns a gitRunner if it can find the binary.
 // It also creats a temp directory for cloning repos.
-func newCmdRunner() (*gitRunner, error) {
+func newCmdRunner(timeout time.Duration) (*gitRunner, error) {
 	gitProgram, err := exec.LookPath("git")
 	if err != nil {
 		return nil, errors.Wrap(err, "no 'git' program on path")
@@ -35,7 +32,7 @@ func newCmdRunner() (*gitRunner, error) {
 	}
 	return &gitRunner{
 		gitProgram: gitProgram,
-		duration:   defaultDuration,
+		duration:   timeout,
 		dir:        dir,
 	}, nil
 }