Update TestPlansAndSuitesMigrationContext Tag mecanism!

[MrHinsh]

Currently when tagging is enabled it is applied to both the Plans and the Suits!

Perhaps we should add an Enum: Plans, PlansAndSuits, None

[ACoderLife]

I noticed this when working on:
#991
I only implemented the AreaPath filter at the plan level, as I wanted all the suites within the plan to be migrated no matter what.

It would be best to have these be consistent.
I also didn't like the requirement of having to tag all the suits to bring them over.

Do you have any examples of users wanting to split up a migration so that a plan is included but no ALL suits under it?
In that case to they give the plan two tags so that the other plans are included in another run?