Always make sure the working directory exists

Always make sure the working directory exists before attempting to run
anything inside of it, and before attempting to copy contents into it or
one of its subdirectories.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

add.go

@@ -50,6 +50,9 @@ func (b *Builder) Add(destination string, extract bool, source ...string) error
 	if destination != "" && filepath.IsAbs(destination) {
 		dest = filepath.Join(dest, destination)
 	} else {
+		if err := os.MkdirAll(filepath.Join(dest, b.Workdir), 0755); err != nil {
+			return fmt.Errorf("error ensuring directory %q exists: %v)", b.Workdir, err)
+		}
 		dest = filepath.Join(dest, b.Workdir, destination)
 	}
 	// Make sure the destination is usable.

run.go

@@ -108,6 +108,9 @@ func (b *Builder) Run(command []string, options RunOptions) error {
 	if spec.Process.Cwd == "" {
 		spec.Process.Cwd = DefaultWorkingDir
 	}
+	if err := os.MkdirAll(filepath.Join(mountPoint, b.Workdir), 0755); err != nil {
+		return fmt.Errorf("error ensuring working directory %q exists: %v)", b.Workdir, err)
+	}
 	mounts := options.Mounts
 	for _, specMount := range spec.Mounts {
 		override := false