twister: Fix execution of twister in makefile environment
twister: Fix execution of twister in makefile environment

When run by a makefile twister might fail to decode the text results of
commands, based upon the environment settings of the system. With this
change escape characters are removed before the string is passed to the
json decoder.

Signed-off-by: Benedikt Schmidt <15c2bbfe1d8dcfe05fdbc9b78c35d10937b406a6@embedded-solutions.at>
finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr