Increase semaphore for molecule job

We thought that some molecule CI test will fail less often if
less molecule jobs would be computed in the same amount of time.
Max server for IBM cloud provider is 25 per host, which means that
maximum value is 50. For sure the host would handle that, but let's
have some resource reservation to avoid potential problems.

Signed-off-by: Daniel Pawlik <[email protected]>

Author: danpawlik

zuul.d/semaphores.yaml

@@ -1,4 +1,4 @@
 ---
 - semaphore:
     name: semaphore-molecule
-    max: 15
+    max: 40