Set execution polling delays correctly

[dpmatthews]

These changes partially address #3706

Tested with this workflow:

[scheduling]
    [[graph]]
        R1 = nolimit & limit95M & limit1H  & limit10M & limit70S
[runtime]
    [[root]]
        script = "echo Hello"
        execution polling intervals = 3*PT30S, PT10M, PT1H
    [[nolimit]]
    [[limit95M]]
        execution time limit = PT95M
    [[limit1H]]
        execution time limit = PT1H
    [[limit10M]]
        execution time limit = PT10M
    [[limit70S]]
        execution time limit = PT70S

Result using master:

$ grep "execution timeout" ~/cylc-run/bug.polling-intervals/runN/log/workflow/log
2022-04-29T15:45:33+01:00 INFO - [1/limit10M running job:01 flows:1] health: execution timeout=PT20M, polling intervals=20*PT30S,PT1M,PT2M,PT7M,...
2022-04-29T15:45:33+01:00 INFO - [1/limit1H running job:01 flows:1] health: execution timeout=PT1H10M, polling intervals=3*PT30S,5*PT10M,PT9M30S,PT2M,PT7M,...
2022-04-29T15:45:33+01:00 INFO - [1/limit70S running job:01 flows:1] health: execution timeout=PT11M10S, polling intervals=2*PT30S,PT1M10S,PT2M,PT7M,...
2022-04-29T15:45:33+01:00 INFO - [1/limit95M running job:01 flows:1] health: execution timeout=PT1H45M, polling intervals=3*PT30S,PT10M,PT1H,PT24M30S,PT2M,PT7M,...
2022-04-29T15:45:33+01:00 INFO - [1/nolimit running job:01 flows:1] health: execution timeout=None, polling intervals=3*PT30S,PT10M,PT1H,...

e.g. limit10M has polling intervals=20*PT30S,PT1M,PT2M,PT7M,... which not what we want.

Result using this branch:

$ grep "execution timeout" ~/cylc-run/bug.polling-intervals/runN/log/workflow/log
2022-04-29T15:43:45+01:00 INFO - [1/limit10M running job:01 flows:1] health: execution timeout=PT20M, polling intervals=3*PT30S,PT9M30S,PT2M,PT7M,...
2022-04-29T15:43:45+01:00 INFO - [1/limit1H running job:01 flows:1] health: execution timeout=PT1H10M, polling intervals=3*PT30S,PT10M,PT49M30S,PT2M,PT7M,...
2022-04-29T15:43:45+01:00 INFO - [1/limit70S running job:01 flows:1] health: execution timeout=PT11M10S, polling intervals=2*PT30S,PT1M10S,PT2M,PT7M,...
2022-04-29T15:43:45+01:00 INFO - [1/limit95M running job:01 flows:1] health: execution timeout=PT1H45M, polling intervals=3*PT30S,PT10M,PT1H,PT24M30S,PT2M,PT7M,...
2022-04-29T15:43:45+01:00 INFO - [1/nolimit running job:01 flows:1] health: execution timeout=None, polling intervals=3*PT30S,PT10M,PT1H,...

e.g. limit10M now has polling intervals=3*PT30S,PT9M30S,PT2M,PT7M,... which makes sense.

Requirements check-list

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg and conda-environment.yml.

• Appropriate tests are included (unit and/or functional).
• Already covered by existing tests.
• Does not need tests (why?).

• Appropriate change log entry included.
• No change log entry required (why? e.g. invisible to users).
• No documentation update required.

[hjoliver]

Looks good 🎉

[datamel]

Final review from me (of change to code base - I have accepted the changes to the test). I have reproduced problem on master to ensure fix works. Merging after CI check.

[oliver-sanders]

(checks passed)