RFR: 8148745: [testbug] Test gc/g1/plab/TestPLABPromotion.java fails in nightly

[Michail Chernov]

Hi all,

Could I have a couple of review for this change:

Webrev: http://cr.openjdk.java.net/~mchernov/8148745/webrev.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8148745

Added -XX:MaxTenuringThreshold=1 to achieve objects promotion at every GC.
Added timeout for TestPLABPromotion.java because it can work sufficient 
time with -Xcomp.
Added @requires to exclude test execution with Flight Recorder, because 
test cannot handle case when some additional objects are created before 
or during test running.
Checking of size of promoted objects was changed because difference of 
real allocated objects and promoted can exceed existing limit with big 
heap size.

Thanks
Michail