This permits script functions that could fail to report errors back, so
that the user can handle them if desired. We use an errno-style of
interface. That means script_error() needs to be called after functions
that supports it. It will return either 0 (all OK) or something else
(an error condition).
The commit also modifies the parse_time() function to use the new
interface. First of all, this is useful for users, and secondly we
needed a capability to craft a testbench test.
closes https://github.com/rsyslog/rsyslog/issues/1978
