Allow override of hostname by environment

[iMartyn]

Given that most container management systems will assign a randomly assigned hostname (or at least it is extremely difficult to set), it would be extremely nice if this image could be extended to override the hostname by an env var.

One usecase for this is when you are running the container on kubernetes behind an ELB, the service name is used for the ELB (and also inside kube) so the hostname of the pod does not match it at all.

This is especially annoying when using self-signed certificates and SSSD - sssd does not allow a hostname mismatch on ssl at all and just breaks auth.

Do you tried to run the container with HOSTNAME environment variable set ?

[iMartyn]

I haven't yet, but if it's as simple as that, then probably I'll submit a pull request to the README.md :-)