Report actual error in error message

While debugging a YAML change just now, I found it impossible to work
out what jenkins-projects-checks.py was actually complaining about
without this additional information.  I thought others might benefit
from it too.

Change-Id: I79b8286a3ef74008e5b0927bddb60f9c98b9b629

tools/jenkins-projects-checks.py

@@ -144,6 +144,7 @@ def validate_jobs():
             try:
                 schema(entry)
             except Exception as e:
+                print("Failure: %s" % e)
                 print("Failure in file %s" % job_file)
                 print("Failure parsing item:")
                 print(item)