Fix bad task host selection

It looks like #873 has broken the test battery where the tests concern
bad task hosts.
Merge pull request #875 from matthewrmshin/fix-bad-task-host

Fix bad task host selection
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
Ignore late polling results.
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.
Added a test to check that we ignore late poll results.
Merge pull request #880 from hjoliver/872.ignore-late-poll-results

Ignore late polling results.
Merge branch 'master' into handle-job-vacated-by-sigusr1