Set curl to fail if HTTP servers return a error.

* modules/openstack_project/files/jenkins_job_builder/config/pypi-jobs.yaml:
Use the curl's --fail option to detect some HTTP 400 and 500 errors.
Then check that the file is actually a gzipped file. The two checks are
necessary because some HTTP error codes do not result in a non zero
return from curl even with the --fail option.

Change-Id: I796d2c5767e787e7106040e7ef0098886135e68c
Reviewed-on: https://review.openstack.org/35562
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins