Info command now return non-zero when errors occur

Running the info command will now return a non-zero error code when an error is displayed by the command. This includes `checks.d` errors. The feature was requested by @miketheman.

The difference between the error codes emitted by this command and the error codes emitted by the status command is that the status command simply checks that all of the Agent subprocesses are running, while the info command checks that the subprocesses are running _and_ that all the checks have passed.