Added a timeout to stop requests.get hanging on platforms with no int…

…ernet (SciTools#3284)

* Added a 1 second timout to stop requests.get hanging on the HPC

* Amended comment to be more generic

* Changed 1 second timeout to 10 seconds.

lib/iris/tests/__init__.py

@@ -115,7 +115,9 @@
     NC_TIME_AXIS_AVAILABLE = False
 
 try:
-    requests.get('https://github.com/SciTools/iris')
+    # Added a timeout to stop the call to requests.get hanging when running
+    # on a platform which has restricted/no internet access.
+    requests.get('https://github.com/SciTools/iris', timeout=10.0)
     INET_AVAILABLE = True
 except requests.exceptions.ConnectionError:
     INET_AVAILABLE = False