sanitycheck: better coverage report generation
sanitycheck: better coverage report generation

When generating coverage report:
* Also generate branch coverage
* If the report is properly generated tell user where to find it
* Handle case in which no ztests are run (it would crash before)

Signed-off-by: Alberto Escolar Piedras <52be3174920ed06cbdfbcf9622a1a6c68e942617@oticon.com>

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