sanitycheck: support pre/post flash scripts

This is needed when a board needs to be reset using an external commands
or tools that are not part of the flash command. For example, power
reset or by poking a GPIO header on the board using external wiring.

add post_flash/pre_flash to the platform section in the hardware map.
For example:

- available: true
  connected: true
  id: OSHW000032254e4500128002ab98002784d1000097969900
  platform: reel_board
  post_script: /tmp/post_flash.sh
  pre_script: /tmp/pre_flash.sh
  product: DAPLink CMSIS-DAP
  runner: pyocd
  serial: /dev/ttyACM11

Signed-off-by: Anas Nashif <anas.nashif@intel.com>