Use smaller test collections

[dougbu]

The fix for #41 was intended to be temporary. It worked but had the cost of placing a large number of tests in the same collection, preventing parallel execution of the affected test classes.

Should revert f098836 and instead use [CollectionDefinition(DisableParallelization = true)] for either the original collection or a new collection containing DisplayExtensionsTest, EditorExtensionsTest and any other test class that writes to the ScopeStorage, ViewEngines.Engines or ModelMetadataProviders.Current static properties.

FYI:

• DisableParallelization is a new feature of the xUnit 2.3.0 runtime. It ensures no other test collection (aka test class in most cases) runs in parallel with one using that CollectionDefinition.
• f098836 affected only the System.Web.Mvc.Test test assembly but should check the other assemblies to see if DisableParallelization would help there too i.e. see if only a small subset of the test collections change static properties
• no test assembly has more than one explicit test collection i.e. almost every test class runs in parallel with others
• multiple test assemblies declare a "Uses ScopeStorage or ViewEngines.Engines" test collection but, due to the assembly boundaries, they aren't really the same

[dougbu]

Moving to 3.2.5 and self-assigning since I'll do this as my first try on fixing #125. That is, #125 may be a duplicate of this issue.

[mkArtakMSFT]

Closing as this is not needed and we don't release too often here to be concerned with the time it takes to build.