REGTEST: fix tls_health_checks random failures on MacOS in Travis-CI

Since commit 2eb1c79df ("REGTEST: make the tls_health_checks test much
faster") the build tests randomly fail on MacOS on Travis-CI. Each time
this test is reponsible for the failure, showing huge response times
possibly indicating that the VMs running the tests are sometimes
overloaded. Since this delay directly impacts the whole regtest execution
time everywhere, it's important not to inflate it too much. It was bumped
to 100ms instead of 40, that doesn't add significantly to the perceived
execution time and should be enough for Travis since test reports have
shown around 60-70 ms.

reg-tests/checks/tls_health_checks.vtc

@@ -79,7 +79,7 @@ haproxy h2 -conf {
         timeout client 20
         timeout server 20
         timeout connect 20
-        default-server downinter 1s inter 40 rise 1 fall 1
+        default-server downinter 1s inter 100 rise 1 fall 1
 
     backend be2
         option log-health-checks