abstract: make fibers cancellable

We are going to finish all client (non-system) fibers in the process
of Tarantool shutdown. First we cancel them and then wait for their
finishing. So if the client fibers are not finished Tarantool shutdown
is never finished too.

Currently some of queue fibers can not be finished and we got hang on
integration testing of PR [1]. Let's fix it.

In `queue_state.lua` the only error that can aries on `box.ctl.wait_rw` or
`box.ctl.wait_ro` is `FiberIsCancelled` so we can just drop pcall.

In `utubettl.lua` we just need to fix a typo. Just as already done for
fifottl in  e355387 ("fix fifottl_fiber_iteration error handling")

[1] PR with client fibers finishing on shutdown.
tarantool/tarantool#9604

queue/abstract/driver/utubettl.lua

@@ -169,7 +169,7 @@ local function utubettl_fiber(self)
         if box.info.ro == false then
             local stat, err = pcall(utubettl_fiber_iteration, self, processed)
 
-            if not stat and not err.code == box.error.READONLY then
+            if not stat and not (err.code == box.error.READONLY) then
                 log.error("error catched: %s", tostring(err))
                 log.error("exiting fiber '%s'", fiber.name())
                 return 1

queue/abstract/queue_state.lua

@@ -65,25 +65,21 @@ local function create_state_fiber(on_state_change_cb)
         fiber.self():name('queue_state_fiber')
         while true do
             if current == queue_state.states.WAITING then
-                local rc = pcall(box.ctl.wait_rw)
-                if rc then
-                    current = queue_state.states.STARTUP
-                    log.info('Queue state changed: STARTUP')
-                    -- Wait for maximum upstream lag * 2.
-                    fiber.sleep(max_lag() * 2)
-                    on_state_change_cb(current)
-                    current = queue_state.states.RUNNING
-                    log.info('Queue state changed: RUNNING')
-                end
+                box.ctl.wait_rw()
+                current = queue_state.states.STARTUP
+                log.info('Queue state changed: STARTUP')
+                -- Wait for maximum upstream lag * 2.
+                fiber.sleep(max_lag() * 2)
+                on_state_change_cb(current)
+                current = queue_state.states.RUNNING
+                log.info('Queue state changed: RUNNING')
             elseif current == queue_state.states.RUNNING then
-                local rc = pcall(box.ctl.wait_ro)
-                if rc then
-                    current = queue_state.states.ENDING
-                    on_state_change_cb(current)
-                    log.info('Queue state changed: ENDING')
-                    current = queue_state.states.WAITING
-                    log.info('Queue state changed: WAITING')
-                end
+                box.ctl.wait_ro()
+                current = queue_state.states.ENDING
+                on_state_change_cb(current)
+                log.info('Queue state changed: ENDING')
+                current = queue_state.states.WAITING
+                log.info('Queue state changed: WAITING')
             end
         end
     end)