RFR(M): 8223660: jtreg: Decouple Unsafe from RTM tests

[Gustavo Romero]

Hi,

Could I get reviews for the following change please?

Bug   : https://bugs.openjdk.java.net/browse/JDK-8223660
Webrev: http://cr.openjdk.java.net/~gromero/8223660/v1/

It removes from the RTM jtreg tests the use of Unsafe native methods as
abort provokers in a transaction.

Relying on Unsafe native methods to abort a transaction makes the RTM test
brittle because an Unsafe native method can be converted to non-native at
any time, breaking the RTM tests. This is the second time it happens.

This change removes the use of Unsafe native methods (currently, pageSize()
is used, but is not native anymore) and adds an isolated native method in
library libXAbortProvoker.so for the XAbortProvoker class that will be used
to abort transactions in the RTM tests, turning the RTM jtreg tests more
self-contained and so less brittle.

I tested the change on x86_64 and PPC64, w/ RTM/HTM CPU feature available.

Thank you!

Best regards,
Gustavo