fix multiple secondary in bootanalyze

- append to the list passed from arg intead of setting a new list

bug: 33210752
Test: python packages/services/Car/tools/bootanalyze/bootanalyze.py -r -c packages/services/Car/tools/bootanalyze/config.yaml -n 10
Change-Id: Ie226532a83c821456a51b2a352a3c8eab6ccd708
1 file changed