Split cbus statistics and make it more modular.
arm: prepare box/lua/stat.cc for a move to .c

 * Add FFI bindings to `struct error`
 * Raise `struct error` from lbox_error(L) using lua_error(L)
 * Catch `struct error` in lbox_call() and update diagnostics
 * Move lbox_error() and lbox_call() to src/lua/utils.c
 * Update most places to use lbox_error(L) to raise C++ exception into Lua
 * Prepare to remove pcall wrapper in Tarantool 1.7

Fix a race condition in box/sockete.test, the port
the test is trying to bind to may be busy