The system tests were missing a test that would test tcp-initial-timeout
and tcp-idle-timeout.
This commit adds new "timeouts" system test that adds:
* Test that waits longer than tcp-initial-timeout and then checks
whether the socket was closed
* Test that sends and receives DNS message then waits longer than
tcp-initial-timeout but shorter time than tcp-idle-timeout than
sends DNS message again than waits longer than tcp-idle-timeout
and checks whether the socket was closed
* Similar test, but bursting 25 DNS messages than waiting longer than
tcp-initial-timeout and shorter than tcp-idle-timeout than do second
25 DNS message burst
* Check whether transfer longer than tcp-initial-timeout succeeds
