minor fixes to outlier detection tso unit test

[braingram]

While working on a related issue I noticed a few minor issues with the tso unit test in outlier detection.

• time variability was added to the container data after it was converted to a cube (these don't share memory so the input cube did not have this variability). This PR moves the cube conversion to after the variability is added.
• the test checks that the result and input data match to verify that the input data was not changed. However the input cube and output cube share the same memory. This means any modification of the input data by the step would not cause the test to correctly fail. This PR checks the result against the container used to make the cube (which doesn't share memory).

Importantly these changes don't cause the test to fail so the current step code is both compatible with the time variability and doesn't modify the input data array. The main benefit of this PR is that the test will now catch regressions for these behaviors.

This PR only modifies a unit test so regression tests will not be run.

Checklist for PR authors (skip items if you don't have permissions or they are not applicable)

• [ ] added entry in CHANGES.rst within the relevant release section
• [ ] updated or added relevant tests
• [ ] updated relevant documentation
• [ ] added relevant milestone
• [ ] added relevant label(s)
• [ ] ran regression tests, post a link to the Jenkins job below. How to run regression tests on a PR
• [ ] All comments are resolved
• [ ] Make sure the JIRA ticket is resolved properly

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 59.56%. Comparing base (064208c) to head (d02ac25). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #8623 +/- ## ======================================= Coverage 59.56% 59.56% ======================================= Files 391 391 Lines 39285 39285 ======================================= Hits 23402 23402 Misses 15883 15883 ```

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