extended pmap with kw args

```on_err_retry``` , default ```true```, specifies if pmap should retry a failed task on a different worker.

```on_err_stop``` , default ```false```,  specifies if pmap should not execute any pending tasks in case of an exception an any currently running tasks.

Default values mimic current behavior.

```runtests.jl ``` has been updated to stop on the first error.