Add a new CLI:watch

Terminal1:t1;
Terminal2:t2;

PART1:
-------------[-d] test for data change-----------------------
[t1]:
watch -d /testwatch
[t2]:
set /testwatch mydata
[t1]: result:
WatchedEvent state:SyncConnected
type:NodeDataChanged
path:/testwatch
new data:mydata
----------------------------------------------------------------
[t1]:
watch -d /testwatch
[t2]:
delete /testwatch
[t1] result:
WatchedEvent state:SyncConnected
type:NodeDeleted
path:/testwatch

PART2:
-------------[-c] test for child change-----------------------
[t1]:
watch -c /testwatch
[t2]
create /testwatch/child_1 mydata
[t1] reslut:
WatchedEvent state:SyncConnected
type:NodeChildrenChanged
path:/testwatch
new child list:[child_1]
----------------------------------------------------------------
[t1]:
watch -c /testwatch
[t2]:
delete /testwatch/child_1
[t1]:
WatchedEvent state:SyncConnected
type:NodeChildrenChanged
path:/testwatch
new child list:[]

PART3:
---------------[-e]test for exist watch---------------------
[t2]:
delete /testwatch
[t1]:
watch -e /testwatch
[t2]:
create /testwatch mydata
[t1] result:
WatchedEvent state:SyncConnected
type:NodeCreated
path:/testwatch
----------------------------------------------------------------
[t1]:
watch -e /testwatch
[t2]:
delete /testwatch
WatchedEvent state:SyncConnected
type:NodeDeleted
path:/testwatch
----------------------------------------------------------------
[t1]:
watch -e /testwatch
[t2]:
set /testwatch mydata666666666
[t1]:
WatchedEvent state:SyncConnected
type:NodeDataChanged
path:/testwatch

----------------------------------------------------------------
a test for watching a non-existent key
[t1]:
watch -d /non-existent_key
Node does not exist: /non-existent_key
watch -c /non-existent_key
Node does not exist: /non-existent_key
watch -e /non-existent_key
[t2]:
create /non-existent_key mydata
[t1]:
WatchedEvent state:SyncConnected
type:NodeCreated
path:/non-existent_key
----------------------------------------------------------------
the test for other watchedEvent state: e.g. Disconnected
[t1]:
watch -c /testwatch
#kill the zk server
WatchedEvent state:Disconnected
type:None
path:null