Bail out after an UnknownHostException when connecting to ZooKeeper.
Bail out after an UnknownHostException when connecting to ZooKeeper.

This error is typically caused by an incorrect ZK quorum specification,
most commonly because of a typo or a configuration problem, so retrying
immediately is generally not appropriate.  This closes #5.

Change-Id: Iad714e375fe2ace1a416f4c75cdbe667c7ef09da

tsuna/asynchbase,hzy001/asynchbase,nvoron23/asynchbase,hhshuai/asynchbase,OpenTSDB/asynchbase,SteamShon/asynchbase,adityakishore/asynchbase,mway08/asynchbase,manolama/asynchbase,tempbottle/asynchbase,mapr/asynchbase,hzy001/asynchbase,nvoron23/asynchbase,angushe/asynchbase,Flipboard/asynchbase,Flipboard/asynchbase,Connexity/asynchbase,tempbottle/asynchbase,yuzhu712/asynchbase,adityakishore/asynchbase,pythian/asynchbase,StumbleUponArchive/asynchbase,angushe/asynchbase,SteamShon/asynchbase,yuzhu712/asynchbase,OpenTSDB/asyncbigtable,Connexity/asynchbase,StumbleUponArchive/asynchbase,mapr/asynchbase,manolama/asynchbase,hhshuai/asynchbase,mway08/asynchbase,OpenTSDB/asynchbase,tsuna/asynchbase,manolama/asyncbigtable