--config flag doesnt work when launching jobs

this won't work and will error out if there's no default cloudexec.toml to use:
`cloudexec launch --config ./tickoverflowsafety.toml --size c-8`

However this works:
`cloudexec launch --size c-8 ./tickoverflowsafety.toml`

The help prompt for cloudexec launch says you gotta use the --config flag, so IMO we just need to update that

I also noticed that sometimes the positional parameter is ignored if there's a cloudfuzz.toml in the current directory. That might be an actual bug