openshift: improve compatibility

[blazdivjak]

This pull request includes updates for Openshift compatibility.

Tested:

• Openshift 3.11
• Kubernetes v1.10.11

Includes:

• update container image permissions and user handling
• update helm chart deployment docs
• add security context related docs to Helm chart values

Container images: https://hub.docker.com/r/blazdivjak/docker-vernemq

[dergraf]

@blazdivjak Sorry for the delay, but thanks for the contribution. To be honest we don't know a lot about Openshift, maybe others from the community could step in to review this. cc @drf @francois-travais @codeadict

[loldiges]

I like the changes you did. I did not use helm or the deployments but your changes to the Dockerfiles work perfectly and deploy on Openshift without root or any other extra-permissions. I will not add a review and leave this to the contributers mentioned above.

[drf]

Sorry for being late to the party. However, the changes are sound to me, but I wonder whether this has been tested outside OpenShift given the various permission changes (apparently shouldn't be an issue, but better safe than sorry). So thumbs up, especially if somebody tested this on standard k8s :)

[blazdivjak]

I did test it on k8s as well. Not extensively however.

[ioolkos]

@greggiles thanks a lot for your testing and vote to merge this. @dergraf merge? @ertanden given your experience, could you give a comment on this?

[ertanden]

@ioolkos this looks good to me.

Maybe a small comment, instead of adding the new file uid_entrypoint, we could also put the content of it at the beginning of the start_vernemq script. It would simplify things I guess.