Gracefully exit when depositor is not able to fetch communities (probably because b2share is down).

depositor/b2share.py

 """a b2share depositor."""
 from furl import furl
-
+from requests.exceptions import ConnectionError
 import json
 import logging
 import requests
@@ -88,8 +88,13 @@ class Depositor:
         communitynames = {}
         communityids = {}
         # verify=False is needed while using fsd-cloud9 with self signed cert
+        try:
             r = requests.get(self.b2shareurl + "communities/",
                              params=self.url_params, verify=self.insecure_ssl)
+        except ConnectionError:
+            logging.error('B2SHARE at {} currently not available'.format(
+                self.b2shareurl))
+            exit(1)
         i = 0
         for community in r.json()['hits']['hits']:
             communitynames.update({i: community['name']})