Support flash from local files for auto_flash_from_pvt.sh.
added `-l | --local` option
added new variable `DL_DIR` which rule is `pvt/{DEVICE_NAME}/{VERSION_NAME}/{USR_ENG}/{BUILD_ID}`
Merge pull request #92 from askeing/support_flash_from_local_files

Support flash from local files for auto_flash_from_pvt.sh.