Default to HOME env var if unable to get via os.User

Fixes the situation where strongbox is compiled without CGO and statically
linked. On Linux user.Current() isn't implemented, so we attempt to
figure out HOME via env vars.

strongbox.go

@@ -54,11 +54,20 @@ func main() {
 	flag.Parse()
 
 	// Set up keyring file name
+	home := ""
 	u, err := user.Current()
 	if err != nil {
-		log.Fatal(err)
+		// Possibly compiled without CGO and syscall isn't implemented,
+		// try to grab the environmet variable
+		home = os.Getenv("HOME")
+		if home == "" {
+			log.Fatal("Could not call os/user.Current() or find $HOME. Please recoming with CGO enabled or set $HOME")
+		}
+	} else {
+		home = u.HomeDir
 	}
-	kr = &fileKeyRing{fileName: filepath.Join(u.HomeDir, ".strongbox_keyring")}
+
+	kr = &fileKeyRing{fileName: filepath.Join(home, ".strongbox_keyring")}
 
 	// only a single flag has been set
 	if flag.NFlag() != 1 {