cylc.job_submission.job_submit: improve pylint score

This pull request contains changes that I have done as part of the log and work restructure change, but should really be separate.

The change is mainly to increase the pylint score and pep8 compliance for `cylc.job_submission.job_submit`.

I have also introduced a small change in `cylc.task_types.task.py` to create the remote job log directory at the point when it installs the suite contact environment file. (This prevents job submission failures when we have `mkdir -p` race condition - which can happen quite regularly on our AIX system.)
:warning: PEP8 violation :warning:
> Imports should be grouped in the following order:
    * standard library imports
    * related third party imports
    * local application/library specific imports

(who died and made me the style police! :-)