Remote carbonlink fix

Accessing metric when on remote server throws exception.

Thu Feb 28 13:35:38 2013 :: Exception Caught
Traceback (most recent call last):
  File "/opt/graphite/webapp/graphite/render/datalib.py", line 226, in fetchData
    cachedResults = CarbonLink.query(dbFile.real_metric)
  File "/opt/graphite/webapp/graphite/render/datalib.py", line 135, in query
    results = self.send_request(request)
  File "/opt/graphite/webapp/graphite/render/datalib.py", line 158, in send_request
    conn = self.get_connection(host)
  File "/opt/graphite/webapp/graphite/render/datalib.py", line 125, in get_connection
    connection.connect( (server, port) )
  File "<string>", line 1, in connect
error: [Errno 111] Connection refused

or if no local carbon-cache:

Fri Feb 22 13:47:00 2013 :: Exception Caught
Traceback (most recent call last):
  File "/opt/graphite/webapp/graphite/render/datalib.py", line 226, in fetchData
    cachedResults = CarbonLink.query(dbFile.real_metric)
  File "/opt/graphite/webapp/graphite/render/datalib.py", line 135, in query
    results = self.send_request(request)
  File "/opt/graphite/webapp/graphite/render/datalib.py", line 157, in send_request
    host = self.select_host(metric)
  File "/opt/graphite/webapp/graphite/render/datalib.py", line 109, in select_host
    return self.hash_ring.get_node(metric)
  File "/opt/graphite/webapp/graphite/render/hashing.py", line 83, in get_node
    index %= len(self.ring)
ZeroDivisionError: integer division or modulo by zero

I stop trying to pull data from carbon-cache if the metric is found on a remote server since the local carbon-cache is it exists doesn't contains data about this metric.