Refactor to show it is onPrepare

Signed-off-by: sguan <sguan@actuate.com>
Merge remote-tracking branch 'upstream/master'
Internal api enhancement

Signed-off-by: sguan <sguan@actuate.com>
Enhance API to take only two argument on image unique file name

Signed-off-by: sguan <sguan@actuate.com>
Merge pull request #52 from sguan-actuate/master

Internal refactor apis for enchancement