cbq_bridge: Fix partition id used for creating single partition index

We use hash partition container for mapping partition keys to partition.
If there is only single partition, that means any partition key should
be mapped to partition 0.

Change-Id: I033b9ab92e96805faff2f74fd287777a56702fe3
Reviewed-on: http://review.couchbase.org/43245
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: Sarath Lakshman <sarath@couchbase.com>