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'
Tiny fix for virt-lxc-convert: we are setting memory values in bytes, while
free may give us values in a different unit by default: force free to output
bytes with -b flag.