Add tests for box.net.box race condition.

 + memory leak in box.net.box (timeouted responses)
 + remote:ping() never throw exception
Merge branch 'stable' of github.com:tarantool/tarantool

Conflicts:
	src/box/lua/box_net.lua
	test/box/ipc.test
	test/box/net.box.result
Merge branch 'master' of github.com:tarantool/tarantool