agent integration tests are flaky

[pablochacin]

Table-driven HTTP and gRPC fault injection integration tests sometimes fail.

If they are run sequentially, they generally pass.

The issue seems to be that sometimes the test checks for the fault injection before the agent has injected the iptables rules that redirect the traffic. Adding a delay before checking the fault injection improves the chances of the test passing.

The solution would be to check the agent has effectively installed the iptable rules. However, the agent is not generating any log message that could be checked in the tests #175