spec: Automatically apply all patches with git

spec: Automatically apply all patches with git

With this change, any patch declared in libvirt.spec with Patch[0-9]* is
automatically applied in %prep. Unlike with the standard %patch[0-9]*,
patches are applied with "git am" to avoid some unexpected results.
However, as a result of this, all patches must be in the right format
for "git am" to be able to apply them; they should ideally be generated
from git using "git format-patch".

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>