bug#26716: Test nginx configuration

[Julien Lepiller]

Hi, here are two patches to react to Christopher's experience. I added
two simple tests that check the presence of the certificate and the key
passed to nginx configuration.

If the error log file cannot be created at startup, error messages
about the configuration file are logged only on stderr. The second
patch makes sure the log file can be created.

0001-gnu-services-nginx-Test-certificate-presence.patch
Description: Text Data

0002-gnu-services-Create-logs-directory.patch
Description: Text Data