tests: add auto-load safe-path init command to gdb

Running make check from a fresh Ubuntu gave the following error message

    TEST tracing_smoke_test
    warning: File "/home/elazar/dev/osv/scripts/loader.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".

Signed-off-by: Elazar Leibovich <elazarl@gmail.com>