HTTP/2 stress test timeout

Motivation:
The stress tests have been observed to fail on the CI server. The average run time of the stress tests has recently been 26+ seconds.  Our timeout is currently set to 30 seconds.

Modifications:
Increase the timeout for the stress test so when the leak profile is active we will have more time to complete the test (with the additional overhead).

Result:
Stress tests fail less frequently (hopefully not at all).