let delay node handle both flush then reset

[dceejay]

and add tests

• [x] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)

Proposed changes

Now that we support a numeric parameter for flush (rather than flush all) - then it now makes sense that if the users specifies flush and reset that we honour the flush part before the reset. (Current behaviour is to ignore the flush and just reset). This PR fixes that so the flush occurs first. And adds tests.

Checklist

• [x] I have read the contribution guidelines
• [x] For non-bugfix PRs, I have discussed this change on the forum/slack team.
• [x] I have run grunt to verify the unit tests pass
• [x] I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage increased (+0.004%) to 68.186% when pulling fc657ecc717be7ea5e199a2e042e915d2ef02046 on delay-flush-reset into 313bab37e2e138e3be43fdb2bfc53138eda6ed59 on dev.