Trivial: typo & redundant log
 - typo: masterctx instead of workerctx
 - redundant log when wrapper task waking up
remove stream sd_lock & mailbox cleanup for master
 - to keep track neighbour, stream sd_lock is no longer needed. Instead,
   use list of free stream & stream desc to avoid accessing to freed
   memory.
 - since master destroy zombie task, there will be the case that master
   get terminate message before get those zombie task. So, need to clean
   up mailbox of master before terminating it
Merge pull request #23 from nguyenvuthiennga/master

modify strategies to keep track task neighbourship