add UnmountAll function to OTA script; support radio images w/path

Three unrelated changes:

- change the add-radio-file makefile function to support adding files
  with paths.  (The path part of the pathname is stripped off.)

- add an UnmountAll function to the OTA script generation code, so
  that we can explicitly unmount everything we've mounted (in addition
  to doing it automatically at the end of the script).

- add the updater API version to the info object passed to
  device-specific code.

Change-Id: Ia62b15403c1cc8fce8d9910f291450c8077e49f4