RFR: 8152896: Convert PrintCompressedOopsMode to Unified Logging

[Rachel Protacio]

Hello,

Please review this change, converting -XX:+PrintCompressedOopsMode to 
-Xlog:gc+heap. The existing diagnostic flag has been aliased to the info 
level of this tagset (for the "Heap address" message that for example 
appears in the hs_err file), and there are both debug and trace levels 
of logging available as well, as per our established schema for 
assigning levels.

Bug: https://bugs.openjdk.java.net/browse/JDK-8152896
Open webrev: http://cr.openjdk.java.net/~rprotacio/8152896.00/

Passes JPRT and RBT quick/non-colo tests.

Thanks!
Rachel