Description of problem:
The RateLimitRestAndUITest.canLimitConcurrentRestRequestsPerAPIKey test is unstable.  It depends on Zanata being too slow to handle the series of requests thrown at it, but if it's fast enough (or the test events are too slow) the test will fail.

Version-Release number of selected component (if applicable):
3.6

How reproducible:
Intermittent

Additional info:
Error Message

Expecting:
 <[201, 201, 201, 201, 201]>
to contain:
 <[201, 201, 201, 201, 429]>
but could not find:
 <[429]>
Stacktrace

java.lang.AssertionError: 
Expecting:
 <[201, 201, 201, 201, 201]>
to contain:
 <[201, 201, 201, 201, 429]>
but could not find:
 <[429]>

at org.zanata.feature.misc.RateLimitRestAndUITest.canLimitConcurrentRestRequestsPerAPIKey(RateLimitRestAndUITest.java:259)