scripts: zephyr_flash_debug.py: swallow exceptions by default
scripts: zephyr_flash_debug.py: swallow exceptions by default

For readability, swallow exceptions unless --verbose is given on the
command line. Add a printline to direct the user how to ensure that's
set in case more information out of the flash script is desired.

Signed-off-by: Marti Bolivar <fd5da480b758a78208111e6ae5c6806e1f887137@opensourcefoundries.com>

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