concurrent_hash_map: implement my_mask without v<>

my_mask is a variable which is reinitialized on each process
restart. Until now, v<> was used for this purpose. Because v<> is not
productized yet, reinitialize my_mask in runtime_initialize() method. Now,
runtime_initialize() MUST be called after proccess restart.

In future, when v<> is productized, we may switch back to using it.