8155951: VM crash in nsk/jvmti/RedefineClasses/StressRedefine: assert failed:...

8155951: VM crash in nsk/jvmti/RedefineClasses/StressRedefine: assert failed: Corrupted constant pool
8151066: assert(0 <= i && i < length()) failed: index out of bounds

Lock classes for redefinition because constant pool merging isn't thread safe, use method constant pool because constant pool merging doesn't make equivalent cpCaches because of invokedynamic

Reviewed-by: sspitsyn, dholmes