Admin() does not work unless the default bucket exist

Problem
Can't connect to the cluster using the Admin class unless there is a bucket called default.

Steps to reproduce

1. Run the following code, against a cluster with no bucket called default:

   from couchbase.admin import Admin

   admin = Admin('Administrator', 'password', host='localhost', port=8091)

   Get the following error:

   ---------------------------------------------------------------------------

   _BucketNotFoundError_0x19 (generated, catch BucketNotFoundError)Traceback (most recent call last)

   <ipython-input-22-59405169434c> in <module>()

   ----> 1 admin = Admin('Administrator', 'password', host='localhost', port=8091)

   /usr/local/lib/python2.7/site-packages/couchbase/admin.pyc in __init__(self, username, password, host, port, **kwargs)

   82 })

   83 super(Admin, self).__init__(**kwargs)

   ---> 84 self._connect()

   85

   86 def http_request(self,

   _BucketNotFoundError_0x19 (generated, catch BucketNotFoundError): <RC=0x19[The bucket requested does not exist], There was a problem while trying to send/receive your request over the network. This may be a result of a bad network or a misconfigured client or server, C Source=(src/bucket.c,785)>