utils: Add utility functions guestfs___concat_strings and guestfs__join_strings.

These concatenate strings or join them with a separator in between.
Augeas >= 1.0.0 is now required.
inspection: Fix hostname inspection because of faulty Augeas path expression (RHBZ#975412).
inspection: Replace phony XML with virt-inspector output from real guests.

Also add an example from a real RHEL 6 guest.

Remove rules for building these XML files which are no longer
relevant.  These files were built by running virt-inspector on real
guests, and then edited to remove excessive <application> sections.
inspector: Add a real test of inspection.

Verify that the output from inspection doesn't change, in order to
catch regressions such as RHBZ#975412.