Support bind mount for Dockerfile's VOLUME command

Current VOLUME command in a Dockerfile cannot bind mount with a host
directory.  Add support it to the VOLUME command too so that users can
specify something like below in their Dockerfile:

  VOLUME  /this/is/host/dir:/container/foo
  VOLUME  /another/host/dir:/container/bar:ro

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Add a test case for bind mount with VOLUME command

Signed-off-by: Namhyung Kim <namhyung@gmail.com>