examples: Use one top level makefile

Using one Makefile per example subdirectory essentially serializes 'make'
calls. Convert to one example/Makefile that builds and distributes
all the subdir files. This reduces example/ rebuild time from about 5.8
seconds to 1.5 seconds on my machine.

One slight difference is that we no longer ship Makefile.am with the
examples in the rpm. This was virtually useless anyways since the Makefile
was very specific to libvirt infrastructure, so wasn't generically
reusable anyways.

Tested with 'make distcheck' and 'make rpm'

examples/lxcconvert/Makefile.am

@@ -1,18 +0,0 @@
-## Copyright (C) 2014 SUSE LINUX Products GmbH, Nuernberg, Germany.
-##
-## This library is free software; you can redistribute it and/or
-## modify it under the terms of the GNU Lesser General Public
-## License as published by the Free Software Foundation; either
-## version 2.1 of the License, or (at your option) any later version.
-##
-## This library is distributed in the hope that it will be useful,
-## but WITHOUT ANY WARRANTY; without even the implied warranty of
-## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-## Lesser General Public License for more details.
-##
-## You should have received a copy of the GNU Lesser General Public
-## License along with this library.  If not, see
-## <http://www.gnu.org/licenses/>.
-
-EXTRA_DIST=				\
-	virt-lxc-convert