Don't ship generated python/libvirt.? files.

Don't ship generated python/libvirt.? files.

libvirt.c and libvirt.h are auto-generated files. Mentioning their names
in *_SOURCES includes them in the distribution. During an out-of-tree
build these shipped files are included instead of the auto-generated
version, potentially breaking the build (as it happend in 0.8.0, because
the shipped libvirt.h was missing the declaration for
'libvirt_virDomainUpdateDeviceFlags')

Use the nodist_*_SOURCES automake variable instead.

Signed-off-by: Philipp Hahn <hahn@univention.de>