PYCBC-78: Fix response.json incompatibility with requests module v1.0+

Change-Id: I0b2fbd1c89bdd22eb98c9bed4e109bcc67fe90b0
Reviewed-on: http://review.couchbase.org/23851
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Reviewed-by: John C. Zablocki <john@couchbase.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>