Fix AxisTest#submitInvalidAxisValue for plugin BOM

[MarkEWaite]

Fix AxisTest#submitInvalidAxisValue for plugin BOM

jenkinsci/bom#615 describes the problem in more detail.

When the git plugin is loaded along with the matrix project plugin, there are multiple input fields on the job configuration page with the name _.name. The previous code waited until there was at least one input field with the name _.name, but instead it needs to wait for the arrival of an additional input field with the name _.name.

Adds a new setName method that sets the value of the _.name field that was created by this plugin. Previously, it would set the first _.name field. Setting the first _.name field works when running the matrix plugin tests without the git plugin loaded, but fails when the git plugin is loaded.

The combination of waiting for the correct _.name field to appear and setting the value on the correct _.name field allows one of the four tests to pass when the git plugin is loaded. The remaining tests need more investigation to pass when the git plugin is loaded.

Also removes a nearly silent skip of the tests when the input does not appear within the timeout.

Also increases the time between retries so that my fast computer needs only two or three retries. I confirmed on a much slower computer (Intel Core i5-2410M CPU @ 2.30GHz) that even on that slow computer, it found the necessary field in 8 tries or less. The upper bound of 18 tries should be more than enough for all the test environments. The new upper bound on time is 306ms, while the previous upper bound was 300ms. The difference between the two values should not be relevant.

The retry period should not be increased beyond the current ~300ms because one of the tests is using an input form that does not include _.name. That test falls through to the end of the retry period.

Testing done

Confirmed that the tests pass on several different performance Linux computers.

Confirmed that one previously failing test AxisTest#submitInvalidAxisValue now passes even when the git plugin is included as a test dependency.

More work will be needed to fix the other AxisTest failures when the git plugin is loaded.

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