CentOS support for ansible deployments

[ksatzke]

Currently, for set-ups of KNIX on localhost, or a single remote host, or a cluster of hosts, Ubuntu 18.04 and Debian 9 are the only supported target OS.

I proose to add support to more target OS, such as CentOS.

The required changes should be done in the feature/CentOS_support branch.

[iakkus]

I have been running KNIX in single host, bare metal mode on xubuntu 18.04 and now xubuntu 20.04 for a while now. No problems encountered about compatibility, except for an SSL package version in xubuntu 20.04.

[ksatzke]

The main difference between Xubuntu and Ubuntu is the desktop environment. Ubuntu is based on the Debian architecture, while CentOS is forked from Red Hat Enterprise Linux which has different package management etc.
I would propose to update KNIX documentation by adding a list of all currently supported OS versions.