[[FEAT]] Dont use err.toString as message

[jmendiara]

Node v6 adds the stacktrace when you call new Error().toString, which will break our test, and probably many logs analyzers that expects a different format

Date are also serialized in other ways

This is the first commit to try to mitigate this

[coveralls]

Coverage remained the same at 100.0% when pulling 6683102 on fix/dontUseToString into a2f1ef0 on develop.

[palmerabollo]

LGTM