Each subdir (common, client and server) can "make dist".
This commit adds configure.ac.shared and autogen.sh to the tar file.
Above files are copied from .. (spice/ directory)
Also added configure.ac.shared (which is not part of "distribution" tarball)
that only imports ../configure.ac.shared such that ./autogen.sh still
works (on "git directories").
Signed-off-by: Uri Lublin <uril@redhat.com>
