Consolidate node XML from sles and redhat into common #391

Stacki uses XML files to describe how to configure Linux systems for both SLES and RedHat. We have a few XML tags that handle things like marking packages for installation, creating files, or executing the tag contents as a script during install time. We call this Stacki Universal XML - SUX.

There are currently two ways of handling cases where this logic actually needs to vary by distribution - the preferred way is to include a conditional attribute in the tag representing the block. The other method is to have separate files in common/nodes/, vs redhat/nodes/ or sles/nodes. The first method should be preferred and there are examples in the node XML files (for example, common/nodes/barnacle.xml, lines 45-61).

For tech debt reasons, there is way more in the OS specific node files than is required (looking at you logrotate.xml!). In general, the SLES files are newer and should be the preferred "base".

In terms of newcomers to the codebase, there is probably low hanging fruit here, and any contributions would be welcome. We have automated testing in place, but it isn't publicly accessible yet.