Fix import issues for Pytest < 3.4.0

Author: Ivan Ivanou

pytest_reportportal/service.py

@@ -7,7 +7,13 @@
 import pytest
 from _pytest.doctest import DoctestItem
 from _pytest.main import Session
-from _pytest.nodes import File, Item
+
+try:
+    pkg_resources.get_distribution('pytest >= 3.4.0')
+    from _pytest.nodes import File, Item
+except pkg_resources.VersionConflict:
+    from _pytest.main import File, Item
+
 from _pytest.python import Class, Function, Instance, Module
 from _pytest.unittest import TestCaseFunction, UnitTestCase
 from _pytest.warning_types import PytestWarning