Isolating tests from general concurrency

[Gary Adams]

A recent question came up about how the exclusiveAccess.dirs property 
was being used to
prevent concurrent tests from using some critical resource. It appears 
that some of
the hotspot/jtreg/vmTestbase tests were setting the property assuming 
they would get
a concurrency=1 type of behavior.

I'd like to start the discussion about how the current feature works and see
if a new feature might be appropriate for other related use cases.