Update PerfDisableSharedMem with FLAG_SET_ERGO in PerfMemory::create_memory_region

In our production environment, jps can not report running java process in rare cases. We can not tell if create_shared_memory failed at startup or /tmp/hsperfdata_user/pid is accidentally deleted.

PerfDisableSharedMem is set true directly in PerfMemory::create_memory_region, it's better updated with FLAG_SET_ERGO, so jcmd can check vm.flags and tells if create_shared_memory failed at startup time.