sanitycheck: use Unknown instead of N/A for fail reason
sanitycheck: use Unknown instead of N/A for fail reason

Instead of N/A, use Unknown which is more appropriate, N/A does not
really apply here.

Signed-off-by: Anas Nashif <0d9952ec84ac43c159f6b7e7ed99a9080c00dd6e@intel.com>

galak/zephyr,Vudentz/zephyr,finikorg/zephyr,Vudentz/zephyr,finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr