Update base image to CentOS 7

[poikilotherm]

Currently, the base image in use is centos:7.5 instead of centos:7.

This is due to possible problems lurking beyond an update described in IQSS/dataverse#5374.
It might be totally unrelated and just caused by the preparation scripts, but better safe than sorry.

This issue tracks the progress and is used for a switch test. Let's see how this goes.

[pdurbin]

This is probably a good idea. I was just reading this article called "Top ten most popular docker images each contain at least 30 vulnerabilities":

https://snyk.io/blog/top-ten-most-popular-docker-images-each-contain-at-least-30-vulnerabilities/

I guess I'm wondering how often the dataverse-k8s image will need to be rebuilt. I assume the base image is being patched frequently by the operating system vendor (Red Hat, in this case).

[poikilotherm]

Yes it is :-)

I am thinking about switching from Docker Hub Automated Builds to a proper Travis CI job, as Travis offers scheduled rebuilds. A rebuild of all Docker tags every day or every two days could be a good idea... ;-)

Obviously it would be better to even take this further and let a test-suite run to ensure nothing breaks from a OS/base image change.

[poikilotherm]

After testing the image based on centos:7 nothing blew up - just Exceptions unrelated to the base image.