Fix the stat calculation bug in host_info page.

Because total_seconds() returns the seconds with type float, so to use it I have to cast it to int.
Rename simple.proto to monsit.proto
Rename SimpleRequest to ReportRequest.

Also add MemInfo
Collect memory info at client side.
Put the memory info to DB.
Show the memory stat on the host_info page.
Change print stmt to logging
Add RpcClient to manager channels.
Add __del__ method to RpcClient.

In the __del__, all channels will be closed.
Add TcpConnection to handle a single connection.

Now TcpChannel may have many connections in it.
Add a resolve_addr method.
Convert list to tuple when getting channel in client.
Add test for TcpClient.
Add test for resolve_addr