Add duplicate file descriptor to capture stderr

We synchronize the options of two tools: test-run and luatest.
When luatest runs separate tarantool instance it duplicates the streams
thereby we can see logs(warning, error, etc)  and prints. We have added
a context manager to create the same behavior with luatest.

Close tarantool/luatest#308

Author: Oleg Chaplashkin

lib/luatest_server.py

@@ -14,6 +14,7 @@
 from lib.tarantool_server import Test
 from lib.tarantool_server import TestExecutionError
 from lib.tarantool_server import TarantoolServer
+from lib.utils import captured_stderr
 
 
 def timeout_handler(process, test_timeout):
@@ -62,10 +63,8 @@ def execute(self, server):
         project_dir = os.environ['SOURCEDIR']
 
         with open(server.logfile, 'ab') as f:
-            stderr = f
-            if Options().args.show_capture:
-                stderr = sys.stdout
-            proc = Popen(command, cwd=project_dir, stdout=sys.stdout, stderr=stderr)
+            with captured_stderr(f):
+                proc = Popen(command, cwd=project_dir, stdout=sys.stdout, stderr=f)
         sampler.register_process(proc.pid, self.id, server.name)
         test_timeout = Options().args.test_timeout
         timer = Timer(test_timeout, timeout_handler, (proc, test_timeout))

lib/options.py

@@ -37,17 +37,6 @@ def format_help(s):
     return textwrap.dedent(s.lstrip('\n')) + '\n'
 
 
-class DeprecationWarning(argparse._StoreTrueAction):
-    """Сustom definition of the 'store_true' procedure"""
-
-    def __call__(self, parser, namespace, values, option_string=None):
-        color_stdout(
-                "Argument %s is deprecated and is ignored.\n" % self.option_strings,
-                schema='info'
-        )
-        setattr(namespace, self.dest, values)
-
-
 class Options(object):
     """Handle options of test-runner"""
 
@@ -135,13 +124,12 @@ def __init__(self):
                     """))
 
         parser.add_argument(
-                "--verbose",
+                "-v", "--verbose",
                 dest='is_verbose',
-                action=DeprecationWarning,
+                action='store_true',
                 default=False,
                 help=format_help(
                     """
-                    Deprecated.
                     Print TAP13 test output to log.
 
                     Default: false.

lib/utils.py

@@ -372,3 +372,23 @@ def prepend_path(p):
 
 def shlex_quote(s):
     return _shlex_quote(s)
+
+
+class captured_stderr:
+    def __init__(self, logfile):
+        self.prevfd = None
+        self.prev = None
+        self.f = logfile
+
+    def __enter__(self):
+        self.prevfde = os.dup(self.f.fileno())
+
+        os.dup2(sys.stderr.fileno(), self.f.fileno())
+
+        self.preve = sys.stderr
+        sys.stderr = os.fdopen(self.prevfde, "w")
+        return self.f
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        os.dup2(self.prevfde, self.preve.fileno())
+        sys.stderr = self.preve