fix for issue #1106 to prevent chcon from failing on filesystems that do not support SELinux (even in SELinux enabled systems)

Proposed fix for #1106 - Updated error handling and control around SELinux statement to be more tolerant and easier to skip if needed.

I've never messed with Chef before and I've never really written Ruby before so I'm sure that this isn't 100% correct.

Title changed from [WIP] proposed fix for issue #1106 to fix for issue #1106 to prevent chcon from failing on filesystems that do not support SELinux (even in SELinux enabled systems)

I think the issue isn't with the labeling or the logic in omnibus, and I don't think the right action is to actually ignore this block. I think this is a documentation fix, and it has to do with selinux contexts being lost when nfs is remounted (after reboot for example).

I'm working on this myself at the moment, and may have something to share soon.

Here are some links to documentation on what I'm referring to:

• RHEL 6 - Making Context Mounts Persistent

• RHEL 7 - Making Context Mounts Persistent

At the moment, I'm just trying to verify the correct context to pass in the options for /etc/fstab for gitlab mounts.