sww tests: wait for every starting line as long as the start takes (closes #331)

Each test in internal/sww that waits for the starting line now waits until
the line is written or sww exits, so a slow Core Rule Set compile on a
loaded host no longer fails it. The two tests that run sww as a child
process get its exit status from a goroutine that waits on it, and no
longer kill it after 30 seconds; the waits after SIGTERM still end after
waitLimit. startRProxyProcess returns a stop function in place of the
process and its output.

Model: opus-5-5

internal/sww/healthcheck_test.go

@@ -41,7 +41,7 @@ func TestHealthCheckInWAFsContainer(t *testing.T) {
 		exited <- run(ctx, settings, out)
 	}()
 
-	addr, _ := out.line(t, "msg", "starting")["address"].(string)
+	addr, _ := out.lineBeforeExit(t, "starting", exited)["address"].(string)
 	_, port, _ := net.SplitHostPort(addr)
 
 	// The container's settings: an address to listen on with an empty