api: ConnectionPool support for Python 3.6

After backporting dataclasses, it became possible to use
ConnectionPool on Python 3.6.

Follows #196

Author: DifferentialOrange

Diff for: CHANGELOG.md

@@ -135,6 +135,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
     ```
 
 - Support iproto feature discovery (#206).
+- Backport ConnectionPool support for Python 3.6.
 
 - Support pandas way to build datetime from timestamp (PR #252).
 

Diff for: tarantool/__init__.py

@@ -40,6 +40,8 @@
     Interval,
 )
 
+from tarantool.connection_pool import ConnectionPool, Mode
+
 try:
     from tarantool.version import __version__
 except ImportError:
@@ -136,9 +138,5 @@ def connectmesh(addrs=({'host': 'localhost', 'port': 3301},), user=None,
 
 __all__ = ['connect', 'Connection', 'connectmesh', 'MeshConnection', 'Schema',
            'Error', 'DatabaseError', 'NetworkError', 'NetworkWarning',
-           'SchemaError', 'dbapi', 'Datetime', 'Interval', 'IntervalAdjust']
-
-# ConnectionPool is supported only for Python 3.7 or newer.
-if sys.version_info.major >= 3 and sys.version_info.minor >= 7:
-    from tarantool.connection_pool import ConnectionPool, Mode
-    __all__.extend(['ConnectionPool', 'Mode'])
+           'SchemaError', 'dbapi', 'Datetime', 'Interval', 'IntervalAdjust',
+           'ConnectionPool', 'Mode']

Diff for: test/suites/lib/skip.py

@@ -122,14 +122,6 @@ def skip_or_run_varbinary_test(func):
                                       'does not support VARBINARY type')
 
 
-def skip_or_run_conn_pool_test(func):
-    """Decorator to skip or run ConnectionPool tests depending on
-    the Python version.
-    """
-
-    return skip_or_run_test_python(func, '3.7',
-                                   'does not support ConnectionPool')
-
 def skip_or_run_decimal_test(func):
     """Decorator to skip or run decimal-related tests depending on
     the tarantool version.

Diff for: test/suites/test_pool.py

@@ -13,7 +13,7 @@
     PoolTolopogyWarning,
 )
 
-from .lib.skip import skip_or_run_sql_test, skip_or_run_conn_pool_test
+from .lib.skip import skip_or_run_sql_test
 from .lib.tarantool_server import TarantoolServer
 
 
@@ -75,7 +75,6 @@ def setUpClass(self):
         print(' POOL '.center(70, '='), file=sys.stderr)
         print('-' * 70, file=sys.stderr)
 
-    @skip_or_run_conn_pool_test
     def setUp(self):
         # Create five servers and extract helpful fields for tests.
         self.servers = []

Diff for: test/suites/test_ssl.py

@@ -10,7 +10,6 @@
     SSL_TRANSPORT
 )
 import tarantool
-from .lib.skip import skip_or_run_conn_pool_test
 from .lib.tarantool_server import TarantoolServer
 
 
@@ -291,7 +290,6 @@ def __init__(self,
 
     @unittest.skipIf(sys.platform.startswith("win"),
                      'Pool tests on windows platform are not supported')
-    @skip_or_run_conn_pool_test
     def test_pool(self):
         servers = []
         cnt = 5