Make CouchbaseClientTests more resilient.

Change-Id: I7476a1dc625000669d40f4f707e5c9003508fe11
Reviewed-on: http://review.couchbase.org/29467
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>