Check and possibly rethink blanket `except`s

[aaaaalbert]

(It is known)[https://docs.python.org/2/howto/doanddont.html#except] that non-specific except: clauses cause opaque problems. We should carefully check the clearinghouse code base's use of this construct, see

$ grep -rl except: *
backend/backend_daemon.py
common/api/keygen.py
common/api/maindb.py
deploymentscripts/deploy_clearinghouse.py
lockserver/lockserver_daemon.py
node_state_transitions/node_transition_lib.py
node_state_transitions/transition_canonical_to_onepercentmanyevents.py
polling/check_active_db_nodes.py
website/html/views.py
website/xmlrpc/views.py