test: wait until server is ready

Current `wait_until_started` method wait till `box.info.status` is
"running" and start sending requests. Such approach is wrong: status
"running" [1] does not guarantees that instance is available for writing
(like creating new users) [2]. It results in flaky test results (for
example, see 4 restarts in [3]).

This patch fixes the issue. After this patch, it is guaranteed that
after `wait_until_ready` call instance had finished to run its
initialization script, including box.cfg, and available for writing data
if it is expected to be able to.

Windows instances use a separate lock mechanism, so this patch is not
related to Windows instances.

1. https://github.com/tarantool/tarantool/blob/983a7ec215d46b6d02935d1baa8bbe07fc371795/src/box/box.cc#L5425-L5426
2. https://github.com/tarantool/tarantool/blob/983a7ec215d46b6d02935d1baa8bbe07fc371795/src/box/box.cc#L5454
3. https://github.com/tarantool/tarantool/actions/runs/5759802620

Author: DifferentialOrange

test/suites/box.lua

@@ -19,3 +19,5 @@ box.cfg{
     pid_file     = "box.pid",
     auth_type    = (auth_type:len() > 0) and auth_type or nil,
 }
+
+rawset(_G, 'ready', true)

test/suites/crud_server.lua

@@ -91,3 +91,5 @@ if crud_imported == false or vshard_imported == false then
 else
     configure_crud_instance(primary_listen, crud, vshard)
 end
+
+rawset(_G, 'ready', true)

test/suites/lib/tarantool_server.py

@@ -302,27 +302,22 @@ def prepare_args(self):
 
         return shlex.split(self.binary if not self.script else self.script_dst)
 
-    def wait_until_started(self):
+    def wait_until_ready(self):
         """
-        Wait until server is started.
+        Wait until server is configured and ready to work.
 
         Server consists of two parts:
         1) wait until server is listening on sockets
-        2) wait until server tells us his status
+        2) wait until server finishes executing its script
         """
 
         while True:
             try:
                 temp = TarantoolAdmin('0.0.0.0', self.args['admin'])
-                while True:
-                    ans = temp('box.info.status')[0]
-                    if ans in ('running', 'hot_standby', 'orphan') or ans.startswith('replica'):
-                        temp.disconnect()
-                        return True
-                    if ans in ('loading',):
-                        continue
-
-                    raise ValueError(f"Strange output for `box.info.status`: {ans}")
+                ans = temp('ready')[0]
+                temp.disconnect()
+                if isinstance(ans, bool) and ans:
+                    return True
             except socket.error as exc:
                 if exc.errno == errno.ECONNREFUSED:
                     time.sleep(0.1)
@@ -352,7 +347,7 @@ def start(self):
                                         cwd=self.vardir,
                                         stdout=self.log_des,
                                         stderr=self.log_des)
-        self.wait_until_started()
+        self.wait_until_ready()
 
     def stop(self):
         """