Improve test stability

Add `skip_all` function to skip all tests in a file.
Increase timeout for a suite.
Improve remote passphrase sync logic.
Fix gcylc task insertion (stop cycle was ignored).
Discard tasks that have passed their own stop cycle.

They were being adding to task pool but in the 'held' state, which
could hold up the suite by means of the runahead limit.
Added a test for the insert command (with and without a stop cycle).
Merge pull request #878 from hjoliver/fix-gcylc-task-insertion

Fix gcylc task insertion (stop cycle was ignored).
Merge pull request #879 from hjoliver/discard-tasks-beyond-their-stop-cycle

Discard tasks that have passed their own stop cycle.
Merge pull request #877 from matthewrmshin/improve-test-stability

Improve test stability
Restore support for user-defined job submission methods.
Merge pull request #881 from hjoliver/restore-user-job-submission-methods

Restore support for user-defined job submission methods.
Merge pull request #880 from hjoliver/872.ignore-late-poll-results

Ignore late polling results.
Fix polling on restart for running tasks.
Merge pull request #882 from arjclark/fix.poll_running_on_restart

Fix polling on restart for running tasks.