generator, customize, v2v: Only place generated files in libguestfs or common.

After the proposed split of the libguestfs repo, we will end up with
the following layout:

  libguestfs.git
      common -> git submodule libguestfs-common.git
      generator

  virt-v2v.git
      common -> git submodule libguestfs-common.git

  guestfs-tools.git
      common -> git submodule libguestfs-common.git

The generator will only be able to write to libguestfs directories and
the common directory/submodule.  This is mostly the case already with
only 6 exceptions:

  customize/customize-options.pod
  customize/customize-synopsis.pod
  customize/customize_cmdline.ml
  customize/customize_cmdline.mli
  v2v/uefi.ml
  v2v/uefi.mli

This commit moves these files around so they appear under common/ml*

It is somewhat unsatisfactory because it involves copying files
around, but there are some mitigating factors:

(1) Any changes now give us more freedom to develop faster and thus
clean things up in future.

(2) The v2v/uefi files ought to go away in future anyway.

This is simple code motion and should have no effect on the built
programs or tests.

Makefile.am

@@ -164,6 +164,7 @@ SUBDIRS += common/mlvisit
 SUBDIRS += common/mlxml
 SUBDIRS += common/mltools
 SUBDIRS += common/mlcustomize
+SUBDIRS += common/mlv2v
 if HAVE_LIBVIRT
 SUBDIRS += common/mllibvirt
 endif