scripts/lib/bsp/engine.py: Add error message for wrong input file
Format of properties file is expected to be a simple json detailing properties, if this format fails an exception is thrown. This patch adds a graceful error message to the case when the properties file has a wrong format.
[YOCTO #9750]
Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>