Avoid ImportError when selenium is missing.

Also provide a warning message. Fixes LP bug 1197815

Change-Id: Id7ffaa8820eefd216d2258d56736a65ddb2483c2

horizon/test/helpers.py

@@ -18,6 +18,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import logging
 import os
 import socket
 
@@ -32,8 +33,19 @@ from django import test as django_test
 from django.test.client import RequestFactory
 from django.utils import unittest
 
-from selenium.webdriver.firefox.webdriver import WebDriver
-from selenium.webdriver.support import ui as selenium_ui
+LOG = logging.getLogger(__name__)
+
+
+try:
+    from selenium.webdriver.firefox.webdriver import WebDriver
+    from selenium.webdriver.support import ui as selenium_ui
+except ImportError as e:
+    # NOTE(saschpe): Several distribution can't ship selenium due to it's
+    # non-free license. So they have to patch it out of test-requirements.txt
+    # Avoid import failure and force not running selenium tests.
+    LOG.warning("{0}, force WITH_SELENIUM=False".format(str(e)))
+    os.environ['WITH_SELENIUM'] = ''
+
 
 import mox