Werk #8098: Do not hang core if Carbon server is not resonding

If you connected the Check_MK Micro Core to Carbon (Graphite) and the carbon server was down then the core would hang after a while in a very nasty long TCP timeout. This is been fixed. If carbon is too slow to handle all the data or if the server is hanging then Check_MK uses the available TCP buffer space for queing graph updates and skips then any further updates, while logging a message into cmc.log:

var/log/cmc.log

2014-12-01 17:16:47 [4] Carbon is too slow. Skipping update of xysrv123;Check_MK;system_time

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