race condition in some master callback funcs

[taocp]

example： https://github.com/BaiduPS/tera/blob/master/src/master/master_impl.cc#L1945

if a TS load a tablet success and down, master receives the response and run the callback function but doesn't find ts is down because of message delay, and changes the status of tablet to kReady, then no ts serve the tablet

[lylei]

This issue is assigned to @00k with 3 medallions