Improve error message when handshake fails due to an unreasonably low frame_max presented by the client

[michaelklishin]

Spotted this while running the functional test suite:

{handshake_error,tuning,0,{exit,{amqp_error,not_allowed,"negotiated frame_max = 100 is lower than the minimum allowed value (4096)",'connection.tune'},'connection.tune_ok',[{rabbit_misc,protocol_error,1,[{file,"src/rabbit_misc.erl"},{line,307}]},{rabbit_reader,handle_method0,2,[{file,"src/rabbit_reader.erl"},{line,1122}]},{rabbit_reader,handle_method0,3,[{file,"src/rabbit_reader.erl"},{line,1078}]},{rabbit_reader,handle_input,3,[{file,"src/rabbit_reader.erl"},{line,992}]},{rabbit_reader,recvloop,4,[{file,"src/rabbit_reader.erl"},{line,452}]},{rabbit_reader,run,1,[{file,"src/rabbit_reader.erl"},{line,434}]},{rabbit_reader,start_connection,4,[{file,"src/rabbit_reader.erl"},{line,392}]},{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,240}]}]}}

while this is an edge case (a client tries to negotiate a ridiculously low frame_max) we should log a better error message.