Bug1160869: incorrect fiber call order.
(https://bugs.launchpad.net/tarantool/+bug/1160869)

Lua socket object creates coio object that bind to a current
fiber, after yield it will resume it in a different fiber
context after a complete io operation.

Fix this situation by updating current coio fiber in most
lua socket operations.
coio-fiber-detach: move coio fiber update from lua socket to coio itself.
Merge branch 'master' into coio-fiber-detach
coio-fiber-detach: review fixes.