caddytest: Revise sleep durations

Attempt to reduce flakiness a bit more

Test suite needs to be rewritten.

caddytest/integration/reverseproxy_test.go

@@ -8,6 +8,7 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/caddyserver/caddy/v2/caddytest"
 )
@@ -441,6 +442,7 @@ func TestReverseProxyHealthCheck(t *testing.T) {
 	}
   `, "caddyfile")
 
+	time.Sleep(100 * time.Millisecond) // TODO: for some reason this test seems particularly flaky, getting 503 when it should be 200, unless we wait
 	tester.AssertGetResponse("http://localhost:9080/", 200, "Hello, World!")
 }