ENG-4130: Add ZK version check to host count node.
ENG-4130: Add ZK version check to host count node.

Multiple processes could be racing to modify this ZK node, add version check to
make sure it writes things atomically.

flybird119/voltdb,ingted/voltdb,migue/voltdb,flybird119/voltdb,creative-quant/voltdb,deerwalk/voltdb,paulmartel/voltdb,ingted/voltdb,zuowang/voltdb,ingted/voltdb,kumarrus/voltdb,wolffcm/voltdb,wolffcm/voltdb,paulmartel/voltdb,simonzhangsm/voltdb,deerwalk/voltdb,paulmartel/voltdb,simonzhangsm/voltdb,kobronson/cs-voltdb,VoltDB/voltdb,ingted/voltdb,paulmartel/voltdb,wolffcm/voltdb,kumarrus/voltdb,migue/voltdb,creative-quant/voltdb,zuowang/voltdb,wolffcm/voltdb,kumarrus/voltdb,simonzhangsm/voltdb,flybird119/voltdb,paulmartel/voltdb,wolffcm/voltdb,deerwalk/voltdb,simonzhangsm/voltdb,zuowang/voltdb,flybird119/voltdb,kumarrus/voltdb,flybird119/voltdb,wolffcm/voltdb,creative-quant/voltdb,migue/voltdb,kumarrus/voltdb,paulmartel/voltdb,ingted/voltdb,deerwalk/voltdb,ingted/voltdb,VoltDB/voltdb,VoltDB/voltdb,zuowang/voltdb,zuowang/voltdb,migue/voltdb,kumarrus/voltdb,kobronson/cs-voltdb,creative-quant/voltdb,migue/voltdb,simonzhangsm/voltdb,creative-quant/voltdb,creative-quant/voltdb,kobronson/cs-voltdb,simonzhangsm/voltdb,wolffcm/voltdb,VoltDB/voltdb,kumarrus/voltdb,zuowang/voltdb,zuowang/voltdb,kumarrus/voltdb,zuowang/voltdb,migue/voltdb,kobronson/cs-voltdb,creative-quant/voltdb,kobronson/cs-voltdb,deerwalk/voltdb,flybird119/voltdb,flybird119/voltdb,paulmartel/voltdb,ingted/voltdb,deerwalk/voltdb,creative-quant/voltdb,migue/voltdb,VoltDB/voltdb,kobronson/cs-voltdb,wolffcm/voltdb,simonzhangsm/voltdb,deerwalk/voltdb,VoltDB/voltdb,migue/voltdb,paulmartel/voltdb,flybird119/voltdb,deerwalk/voltdb,ingted/voltdb,kobronson/cs-voltdb,VoltDB/voltdb,simonzhangsm/voltdb,kobronson/cs-voltdb