lib: add a new wrapper function of strdup()

Reviewed-by: Ruoyu <liangry@ucweb.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
dog: duplicate value which is passed via command line for simplyfing cleaning

With this change, vdi_setattr() duplicates value which is passed via
command line with xstrdup(). With this change, dog can free() the
value unconditionally. It makes the intention of the code clear.

Reported-by: Ruoyu <liangry@ucweb.com>
Reviewed-by: Ruoyu <liangry@ucweb.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
cluster/zookeeper: add log information for zk auto-recoonect

Reported-by: Valerio Pachera <sirio81@gmail.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>