Fix Multivariate MODE to log it's output to a single log file.

[JohnHalleyGotway]

Describe the Enhancement

This task is closely related to MET #1283. If all Multivariate MODE functionality is run by a single process, then the logging issue effectively goes away.

MET #1184 was included in the met-10.0.0-beta2 release to add the multi-variate MODE option. This version of the code spawns new processes to execute individual calls to the standard MODE prior to combining the output into a super object. This task is to figure out how to handle the writing of a log file in this context. Since multiple processes are spawned, having them write to the same output log file is non-trivial.

Since the calls to MODE are done sequentially, consider adding a no-clobber option to the logger so that each call to single MODE can open and append to the same log file without overwriting it.

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[JohnHalleyGotway]

Please note that any changes to how Multi-Variate MODE should be run based on this issue should be noted on the METplus issue for the Multi-Variate MODE wrapper (dtcenter/METplus#1585).

[davidalbo]

Closing this issue as it was fixed by refactoring multivariate mode to not spawn multiple instance of traditional mode. The newer design does not do this, it does sequential steps that depend on each other (so the original design no longer made sense).