[leo_gateway] Replace erlang:now with os:timestamp

[mocchira]

Need less to say, erlang:now is slow.

[kanno@leofs11 leofs]$ find deps/leo_* -type f|xargs grep erlang:now
deps/leo_gateway/src/leo_gateway_rpc_handler.erl:    {_,_,NowPart} = erlang:now(),

We will fix the above part.

[yosukehara]

I've found 4 lines as below:

%% leo_gateway:
leo_gateway/src/leo_gateway_rpc_handler.erl:223:    {_,_,NowPart} = erlang:now(),

%% leo_logger:
leo_logger/src/leo_logger_appender_file.erl:52:    {{Y, M, D}, {H, _, _}} = calendar:now_to_local_time(now()),
leo_logger/src/leo_logger_server.erl:300:    {{Y, M, D}, {H, _, _}} = calendar:now_to_local_time(now()),
leo_logger/src/leo_logger_server.erl:320:    {{Y, M, D}, {H, _, _}} = calendar:now_to_local_time(now()),

[mocchira]

@yosukehara thx!

[mocchira]

Fixed with below two commits.
leo-project/leo_gateway@5f4d1cb
leo-project/leo_logger@9e7a30d