Arch Linux clean up

• Stop managing /var folder under Arch
• Removal of Arch defaults that aren't set in the distro

Thanks to @haraldkoch!

Skip package install when Ansible doesn't know the package manager

From PR #47 :

Atomic Host uses unsupported package manager rpm-ostree. So, ansible_pkg_mgr is unknown and this task will fail. sshd is already in base system images. Apart from this, sshd configuration is standard for Fedora/CentOS.

Thanks to @knopki for the fix.

OpenBSD 6.0 support

Merge pull request #44 from jasperla/openbsd

Support for OpenBSD

Add xenial to galaxy meta data

Xenial has been supported since April, but Galaxy meta data didn't reflect that. This PR from @snoopdouglas fixes that.