sheep/http: add macro ONODE_HDR_SIZE

Add macro ONODE_HDR_SIZE to replace BLOCK_SIZE in http with which the
code will be more easier to understand.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
sheep/http: add Created-Time for onode

At present, we allocate space for an onode and then write data for it,
so we should record two times: 'ctime' means when the onode is created
and allocated space, 'mtime' means when the data of onode have all be
written done.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
sheep/cluster: use wrapper function to create ephemeral znode

We use zk_create_node() before, but when operation of creating ephemeral
zonde has been timeout, we will see multi-znodes in parent znode because
zk_create_node() will create znodes again if there is ZOPERATIONTIMEOUT.
Multi-znodes in same directry will make zk_lock() be dead loop.

The best solution for this problem is make value of 'timeout' for
zookeeper_init() bigger, but we still need to use zk_create_seq_node() to
replace zk_create_node() for which we will see "operation timeout" fail
in sheep log.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
sheep/cluster: change output format in sheep log

We have print debug information for 'lock_id' in octal when calling
zk_lock(), so is the zk_unlock().

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>