Add sync.WaitGroup to the payloads buffer test
Add sync.WaitGroup to the payloads buffer test

In order to prevent payloads buffer tests fail intermitently
added syncronization to make sure assertion won't happen before
message appears in the channel.

Change-Id: I141492f87c58cbcecb82b8aa21feafce3da83785
Signed-off-by: Artem Barger <6d127d713cb520aa658cf81ac2373d74ffc1958c@il.ibm.com>

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