Add a runner for contrail-test Juniper tests

- add steps in tcp_tests/templates/opencontrail to prepare tests
- add a fixture and a test runner 'test_opencontrail' that gets
  the two variables from environment to pass them to test runner:

  export OPENCONTRAIL_TAGS=smoke
  export OPENCONTRAIL_FEATURES=neutron

- fix docstrings for fixtures
- add print of the environment variables that can be used in tests
  and current defaults (taking into account the exported variables)
diff --git a/tcp_tests/managers/common_services_manager.py b/tcp_tests/managers/common_services_manager.py
index 7735f9a..a91eb46 100644
--- a/tcp_tests/managers/common_services_manager.py
+++ b/tcp_tests/managers/common_services_manager.py
@@ -26,4 +26,4 @@
     def install(self, commands):
         self.__underlay.execute_commands(commands,
                                          label='Install common services')
-        self.__config.common_services.installed = True
+        self.__config.common_services.common_services_installed = True