examples: Install under $(docdir)

examples: Install under $(docdir)

Our build system doesn't currently install the various
example programs provided along libvirt; however, both the
upstream .spec file and the Debian packaging go out of
their way to make sure these useful demos are included in
the respective documentation packages.

Moreover, doing so without help from the upstream build
system is easy to get wrong: the libvirt-docs RPM package,
for example, ends up missing one of the examples and
including a bunch of empty .deps/ directories.

Install the examples in $(docdir) as part of our regular
procedure, so that users and downstreams don't have to do
anything special about them.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Acked-by: Michal Privoznik <mprivozn@redhat.com>