Enable luatest logging

If the test fails and there is a luatest log file (`run.log` by default)
you'll see the following output:

 - [box-luatest/varbinary_test.lua, null]
  # logfile:         /tmp/t/log/031_box-luatest.log
  # luatest logfile: /tmp/t/031_box-luatest/run.log
  # reproduce file:  /tmp/t/reproduce/031_box-luatest.list.yaml

Closes #427

lib/luatest_server.py

@@ -37,10 +37,10 @@ def __init__(self, *args, **kwargs):
     def execute(self, server):
         """Execute test by luatest command
 
-        Execute `luatest -c --no-clean --verbose <name>_test.lua --output tap`
-        command. Disable capture mode and deletion of the var directory.
-        Provide a verbose output in the tap format. Extend the command by
-        `--pattern <pattern>` if the corresponding option is provided.
+        Execute `luatest -c --no-clean --verbose <name>_test.lua --output tap --log <path>`
+        command. Disable capture mode and deletion of the var directory. Provide a verbose
+        output in the tap format. Extend the command by `--pattern <pattern>` if the
+        corresponding option is provided.
         """
         server.current_test = self
         script = os.path.join(os.path.basename(server.testdir), self.name)
@@ -51,6 +51,8 @@ def execute(self, server):
         command.extend([server.luatest])
         # Add luatest command-line options.
         command.extend(['-c', '--no-clean', '--verbose', script, '--output', 'tap'])
+        # Add luatest logging option.
+        command.extend(['--log', os.path.join(server.vardir, 'run.log')])
         if Options().args.pattern:
             for p in Options().args.pattern:
                 command.extend(['--pattern', p])

lib/worker.py

@@ -69,6 +69,16 @@ def get_reproduce_file(worker_name):
     return os.path.join(reproduce_dir, '%s.list.yaml' % worker_name)
 
 
+def get_luatest_logfile(worker_name):
+    # Luatest logging is only for LuatestServer workers.
+    # It doesn't always guarantee a log file.
+    # If it doesn't exist, it will return None.
+    if 'luatest' in worker_name:
+        path = os.path.join(main_vardir(), worker_name, 'run.log')
+        if os.path.isfile(path):
+            return path
+
+
 def print_greetings():
     # print information about tarantool
     color_stdout('\n')

listeners.py

@@ -14,6 +14,7 @@
 from lib.worker import WorkerOutput
 from lib.worker import WorkerTaskResult
 from lib.worker import get_reproduce_file
+from lib.worker import get_luatest_logfile
 from lib.utils import prefix_each_line
 from lib.utils import safe_makedirs
 from lib.utils import print_tail_n
@@ -161,6 +162,9 @@ def print_tasks_info(self, tasks):
             task_id_str = yaml.safe_dump(task_id, default_flow_style=True)
             final_report('- %s' % task_id_str, schema='test_var')
             color_stdout('# logfile:        %s\n' % logfile)
+            luatest_logfile = get_luatest_logfile(worker_name)
+            if luatest_logfile:
+                color_stdout('# luatest logfile: %s\n' % luatest_logfile)
             reproduce_file_path = get_reproduce_file(worker_name)
             color_stdout('# reproduce file: %s\n' % reproduce_file_path)
             if show_reproduce_content: