Add test for zk; read more than 1kiB data
Modify buffer size to 1MiB
Fix zk::read against data being NULL
Use zoo_exists in zk::read to get buffer size
Fix zk::read against data being empty
Fix error message for zk::read
Rewrite zk::read as loop
Output log when reload in zk::read
fix classname for jsonconfig::config::iterator::key
Merge pull request #624 from gintenlabo/allow-config-file-bigger-than-1kiB

Allow config more than 1kiB in distributed mode (fixes #617)
Merge pull request #647 from jubatus/fix-classref

fix classname for jsonconfig::config::iterator::key
Fix json_test: fixes #636