Improve test result reporting in Styx functional test suite

[mikkokar]

This PR improves test result reporting, especially for failures.

The new TestErrorReporter class listens for Kotlintest lifecycle notifications and logs the results accordingly. The ProjectConfig applies this listener globally for all existing test suites without having to modify existing tests.

This makes the following information available in the Travis logs.

At the start of each spec, it logs:

08:57:12.335 [kotlintest-engine-0 @coroutine#1] INFO  StyxFT - Starting com.hotels.styx.routing.ConditionRoutingSpec

Then, at the beginning of each test:

08:57:12.344 [pool-3-thread-1 @coroutine#2] INFO  StyxFT - Running 'Routes HTTP protocol' - ConditionRoutingSpec.kt:35

And at the end of each passed test:

08:57:12.608 [pool-3-thread-1 @coroutine#5] INFO  StyxFT - Routes HTTP protocol - Success

And at the end of each failed test:

08:57:12.709 [pool-3-thread-1 @coroutine#9] INFO  StyxFT - Routes HTTPS protocol - Failure
08:57:12.709 [pool-3-thread-1 @coroutine#9] INFO  StyxFT - expected: 502 Bad Gateway but was: 200 OK
org.opentest4j.AssertionFailedError: expected: 502 Bad Gateway but was: 200 OK
	at com.hotels.styx.routing.ConditionRoutingSpec$2.invokeSuspend(ConditionRoutingSpec.kt:61)
	at com.hotels.styx.routing.ConditionRoutingSpec$2.invoke(ConditionRoutingSpec.kt)
	at io.kotlintest.runner.jvm.TestCaseExecutor$executeTest$supervisorJob$1$invokeSuspend$$inlined$map$lambda$1.invokeSuspend(TestCaseExecutor.kt:121)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:32)
	at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:233)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:748)

Finally, at the end of each spec:

08:57:12.710 [kotlintest-engine-0 @coroutine#1] INFO  StyxFT - Finished com.hotels.styx.routing.ConditionRoutingSpec