* init etcd cclient
* add etcd
* add etcd.go
* fix compile problem
* move code to etcd.go
* add etcd_lister.go for pserver client
* add etcd_client_test.go
* merge etcd_client_test and client_test
* refine client_test.go
* refine code
* format code
* add TODO and use interface instead of struct
* fix typo of initDesiredPservers
* optimize dir structure of go/pserver/client
* add a flag to config index for pserver
* follow comment
* fix path
* optimize code
* remove err in pserver NewEtcd
* restore comment about /ps_desired
qingqing01
Helin Wang
Qiao Longfei
wuyi05
yi.wu