RFR (XS) 8238247: CTW runner should sweep nmethods more aggressively

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8238247

Candidate fix:
  https://cr.openjdk.java.net/~shade/8238247/webrev.01/

Current CTW runner leaves the just-compiled nmethods behind. At some point the sweeper comes in and
make them go away, stabilizing on some number of nmethods. However, that stabilization point is too
far away for the throwaway compilations CTW runner does.

In the end, this leads to inflation of nmethod and dependencies population, which slows down the
subsequent compiles and deopts. If you have a very large JAR file, it would take days to CTW. With
this patch, it takes a few hours. applications/ctw/modules also improves quite nicely with it. See
the comments in bug report for additional details.

Testing: adhoc CTW runs, make run-test applications/ctw/modules

-- 
Thanks,
-Aleksey