add try/catch for python-louvain (#1842)

added a catch for the test importing an uncommon module

Authors:
  - Brad Rees (https://github.com/BradReesWork)

Approvers:
  - Rick Ratzel (https://github.com/rlratzel)

URL: #1842

python/cugraph/cugraph/tests/test_louvain.py

@@ -28,9 +28,15 @@
 
 with warnings.catch_warnings():
     warnings.filterwarnings("ignore", category=DeprecationWarning)
-    import community
     import networkx as nx
 
+try:
+    import community
+except ModuleNotFoundError:
+    pytest.exit("community module not found\n"
+                "The python-louvain module needs to be installed\n"
+                "please run `pip install python-louvain`")
+
 
 print("Networkx version : {} ".format(nx.__version__))