testall script should fail a .x.cf test if it doesn't print an error

testall script should fail a .x.cf test if it doesn't print errors.

I can't think of any reason why the agent should exit with non-zero without printing an error / critical error.

The testall script is here:

https://github.com/cfengine/core/blob/master/tests/acceptance/testall

Everything needed to do this is probably a grep and an if.