builder/virtualbox: detect vboxmanage errors with zero code [GH-1119]

CHANGELOG.md

@@ -69,6 +69,8 @@ BUG FIXES:
   * builder/virtualbox/all: Seed RNG to avoid same ports. [GH-1386]
   * builder/virtualbox/all: Better error if guest additions URL couldn't be
       detected. [GH-1439]
+  * builder/virtualbox/all: Detect errors even when `VBoxManage` exits
+      with a zero exit code. [GH-1119]
   * builder/virtualbox/iso: Append timestamp to default name for parallel
       builds. [GH-1365]
   * builder/vmware/all: `ssh_host` accepts templates. [GH-1396]

builder/virtualbox/common/driver_4_2.go

@@ -157,6 +157,13 @@ func (d *VBox42Driver) VBoxManage(args ...string) error {
 		err = fmt.Errorf("VBoxManage error: %s", stderrString)
 	}
 
+	if err == nil {
+		m, _ := regexp.MatchString("VBoxManage([.a-z]+?): error:", stderrString)
+		if m {
+			err = fmt.Errorf("VBoxManage error: %s", stderrString)
+		}
+	}
+
 	log.Printf("stdout: %s", stdoutString)
 	log.Printf("stderr: %s", stderrString)