Core: fix step run error logging

[amartinz]

Eh, looks like Winston's default error object handling is just too simple. For an error that apparently kills the run, everything including the stacktrace should be printed and JSON.stringify won't work since the properties are not enumerable.

This looks like the simplest solution: winstonjs/winston#1338 (comment)
Would require also changing this to two log calls (also this feels more like error than debug level imo).

Originally posted by @maciek134 in #2827 (comment)