Update to use go modules (#671)

This includes updates to CI config, vendor files, etc.
I've hard-coded the k8s depedency at 1.13.4 to keep it inline with what
we currently have and to make sure a another run of `go mod tidy`
doesn't accidentally update it to an unexpected version.

Thanks to hectorj2f for carrying this along.

vendor/github.com/mitchellh/go-homedir/README.md

@@ -0,0 +1,14 @@
+# go-homedir
+
+This is a Go library for detecting the user's home directory without
+the use of cgo, so the library can be used in cross-compilation environments.
+
+Usage is incredibly simple, just call `homedir.Dir()` to get the home directory
+for a user, and `homedir.Expand()` to expand the `~` in a path to the home
+directory.
+
+**Why not just use `os/user`?** The built-in `os/user` package requires
+cgo on Darwin systems. This means that any Go code that uses that package
+cannot cross compile. But 99% of the time the use for `os/user` is just to
+retrieve the home directory, which we can do for the current user without
+cgo. This library does that, enabling cross-compilation.

vendor/github.com/mitchellh/go-homedir/go.mod

@@ -0,0 +1 @@
+module github.com/mitchellh/go-homedir

vendor/github.com/mitchellh/go-homedir/homedir.go

@@ -76,34 +76,62 @@ func Expand(path string) (string, error) {
 	return filepath.Join(dir, path[1:]), nil
 }
 
+// Reset clears the cache, forcing the next call to Dir to re-detect
+// the home directory. This generally never has to be called, but can be
+// useful in tests if you're modifying the home directory via the HOME
+// env var or something.
+func Reset() {
+	cacheLock.Lock()
+	defer cacheLock.Unlock()
+	homedirCache = ""
+}
+
 func dirUnix() (string, error) {
+	homeEnv := "HOME"
+	if runtime.GOOS == "plan9" {
+		// On plan9, env vars are lowercase.
+		homeEnv = "home"
+	}
+
 	// First prefer the HOME environmental variable
-	if home := os.Getenv("HOME"); home != "" {
+	if home := os.Getenv(homeEnv); home != "" {
 		return home, nil
 	}
 
-	// If that fails, try getent
 	var stdout bytes.Buffer
-	cmd := exec.Command("getent", "passwd", strconv.Itoa(os.Getuid()))
-	cmd.Stdout = &stdout
-	if err := cmd.Run(); err != nil {
-		// If the error is ErrNotFound, we ignore it. Otherwise, return it.
-		if err != exec.ErrNotFound {
-			return "", err
+
+	// If that fails, try OS specific commands
+	if runtime.GOOS == "darwin" {
+		cmd := exec.Command("sh", "-c", `dscl -q . -read /Users/"$(whoami)" NFSHomeDirectory | sed 's/^[^ ]*: //'`)
+		cmd.Stdout = &stdout
+		if err := cmd.Run(); err == nil {
+			result := strings.TrimSpace(stdout.String())
+			if result != "" {
+				return result, nil
+			}
 		}
 	} else {
-		if passwd := strings.TrimSpace(stdout.String()); passwd != "" {
-			// username:password:uid:gid:gecos:home:shell
-			passwdParts := strings.SplitN(passwd, ":", 7)
-			if len(passwdParts) > 5 {
-				return passwdParts[5], nil
+		cmd := exec.Command("getent", "passwd", strconv.Itoa(os.Getuid()))
+		cmd.Stdout = &stdout
+		if err := cmd.Run(); err != nil {
+			// If the error is ErrNotFound, we ignore it. Otherwise, return it.
+			if err != exec.ErrNotFound {
+				return "", err
+			}
+		} else {
+			if passwd := strings.TrimSpace(stdout.String()); passwd != "" {
+				// username:password:uid:gid:gecos:home:shell
+				passwdParts := strings.SplitN(passwd, ":", 7)
+				if len(passwdParts) > 5 {
+					return passwdParts[5], nil
+				}
 			}
 		}
 	}
 
 	// If all else fails, try the shell
 	stdout.Reset()
-	cmd = exec.Command("sh", "-c", "cd && pwd")
+	cmd := exec.Command("sh", "-c", "cd && pwd")
 	cmd.Stdout = &stdout
 	if err := cmd.Run(); err != nil {
 		return "", err
@@ -123,14 +151,16 @@ func dirWindows() (string, error) {
 		return home, nil
 	}
 
+	// Prefer standard environment variable USERPROFILE
+	if home := os.Getenv("USERPROFILE"); home != "" {
+		return home, nil
+	}
+
 	drive := os.Getenv("HOMEDRIVE")
 	path := os.Getenv("HOMEPATH")
 	home := drive + path
 	if drive == "" || path == "" {
-		home = os.Getenv("USERPROFILE")
-	}
-	if home == "" {
-		return "", errors.New("HOMEDRIVE, HOMEPATH, and USERPROFILE are blank")
+		return "", errors.New("HOMEDRIVE, HOMEPATH, or USERPROFILE are blank")
 	}
 
 	return home, nil