Use datacenter id

Datacenter id is already read from cmap and sent to qnetd, but afterwards it is not used. Implement support at least for fifty-fifty split, so it will possible to handle case with 2 data centers (sites) each with 2 nodes and requirement of 2 nodes must be from same data center. Or other way, cluster shouldn't be quorate if there is 1 node from datacenter A and 1 node from datacenter B.