Test run: Don't print summary if interrupted via CTRL+C (SIGINT) (#564)

Its potentially confusing if we print the summary despite the run having
been interrupted, since the summary will show "context canceled" errors
that someone not familiar with Go terminology won't understand.

Instead, don't print anything, so its more clear the program was stopped
in the middle of its work.

main.go

@@ -200,7 +200,9 @@ func run(ctx context.Context, wg *sync.WaitGroup, globalCollectionOpts state.Col
 					doLogTest(ctx, servers, globalCollectionOpts, logger)
 				}
 
-				selftest.PrintSummary(servers, logger.Verbose)
+				if ctx.Err() == nil {
+					selftest.PrintSummary(servers, logger.Verbose)
+				}
 				success := allFullSuccessful && allActivitySuccessful
 				if success {
 					fmt.Fprintln(os.Stderr, "Test successful")