RFR: Rename OpaqueNode4 to OpaqueNode5

[Aleksey Shipilev]

Hi,

There is a conflict between sh/jdk10 and jdk10/hs: both have OpaqueNode4.
jdk10/hs has it for null-check handling. sh/jdk10 has it for loop strip mining.

I suggest we yield to upstream, and rename our OpaqueNode4 to OpaqueNode5:
  http://cr.openjdk.java.net/~shade/shenandoah/c2-opaque-rename/webrev.01/

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey