Handle ImportError's when quantumclient is missing

Updates tempest/manager.py so that it ignore's ImportError
exceptions when quantumclient is not present.

Not all Tempest tests require a quantumclient so it makes sense not
to require it all the time. If a user tries to run quantum specific
tests they will simply get an error when trying to create the
network client instead should quantumclient not be present.

Change-Id: Iea5476eea91e0d92c3b4728f041a3ce72bb5a320
diff --git a/tempest/manager.py b/tempest/manager.py
index 6487d0c..ce7cf93 100644
--- a/tempest/manager.py
+++ b/tempest/manager.py
@@ -21,7 +21,10 @@
 import glanceclient
 import keystoneclient.v2_0.client
 import novaclient.client
-import quantumclient.v2_0.client
+try:
+    import quantumclient.v2_0.client
+except ImportError:
+    pass
 
 import tempest.config
 from tempest import exceptions