Fixes testcase to accept data payload as json encoded.

Signed-off-by: crynobone <crynobone@gmail.com>
Queue sync driver should create data payload as json (consistent with other driver).

Signed-off-by: crynobone <crynobone@gmail.com>
Merge pull request #3959 from crynobone/patch/queue-sync

Fixes inconsistency when using Queue with sync driver.