Low: tools: Use crm_exit() consistently

There doesn't seem to be a downside. 0c20c323 actually switched from
crm_exit() to exit() in a few places (with no explanation of why). The
only problem I see is that prior to the previous commit, we didn't
NULL-check the known_schemas list before freeing it.

At worst, if nothing has been initialized yet, crm_exit() does some
trivial checks for NULL or boolean values and then exits.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>