do_autogen.sh: --disable-static

This will make builds go ~2x as fast when developing.

Reported-by: Luis Pabon <lpabon@redhat.com>
Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #2025 from ceph/wip-disable-static

do_autogen.sh: --disable-static

Reviewed-by: Loic Dachary <loic@dachary.org>