Makefile: put tests/ under libs-y
Makefile: put tests/ under libs-y

ztest framework doesn't do anything privileged, it interacts with the
kernel using system calls like other application code and should be
considered runtime logic.

Signed-off-by: Andrew Boie <aab045b28152628be6af0e556050d0381fd0a34d@intel.com>

mbolivar/zephyr,galak/zephyr,Vudentz/zephyr,punitvara/zephyr,fbsder/zephyr,explora26/zephyr,explora26/zephyr,nashif/zephyr,fbsder/zephyr,fbsder/zephyr,aceofall/zephyr-iotos,aceofall/zephyr-iotos,aceofall/zephyr-iotos,finikorg/zephyr,finikorg/zephyr,kraj/zephyr,nashif/zephyr,explora26/zephyr,kraj/zephyr,punitvara/zephyr,aceofall/zephyr-iotos,punitvara/zephyr,galak/zephyr,zephyriot/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,mbolivar/zephyr,mbolivar/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,fbsder/zephyr,zephyriot/zephyr,explora26/zephyr,punitvara/zephyr,nashif/zephyr,nashif/zephyr,ldts/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,kraj/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,fbsder/zephyr,zephyriot/zephyr,Vudentz/zephyr,aceofall/zephyr-iotos,Vudentz/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,zephyriot/zephyr,ldts/zephyr,kraj/zephyr,kraj/zephyr,galak/zephyr,ldts/zephyr