modify resolv-conf resource (#27)

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## Description

Modify the resolve.conf template resource so that it removes the
systemd-resolve managed symlink and creates a regular file.

## Context / Why are we making this change?

When chef attempts to update a template that's symlinked, it will update
the source file instead of the file you intend to update.

On Ubuntu, /etc/resolv.conf is symlinked to
/run/systemd/resolve/stub-resolv.conf and managed by systemd-resolved.
Resolve.conf and systemd-resovled both attempt to update the same file,
so it's safe to assume you shouldn't ever be using both at the same
time. If you use resolve.conf, we want to remove this symlink and treat
resolv.conf as a normal file.
 
Both options (`force_unlink` and `manage_symlink_source`) seem to be
needed based on this bug report:
chef/chef#4992

## Testing and QA Plan

Images build and function correctly with these additional options added
to the template resource.

cookbooks/fb_resolv/recipes/default.rb

@@ -27,4 +27,6 @@
   owner node.root_user
   group node.root_group
   mode '0644'
+  force_unlink true
+  manage_symlink_source false
 end