TestEnv: Clean up ftrace conf parsing
TestEnv: Clean up ftrace conf parsing

- Simplify conditional by assuming test_conf is not None
- Use dict.get to simplify conditional

joelagnel/lisa,bjackman/lisa,mdigiorgio/lisa,credp/lisa,arnoldlu/lisa,ARM-software/lisa,ARM-software/lisa,credp/lisa,joelagnel/lisa,ARM-software/lisa,ARM-software/lisa,mdigiorgio/lisa,bjackman/lisa,credp/lisa,credp/lisa,arnoldlu/lisa