Add support for SUSE build on build.opensuse.org

This matches the SUSE build work for calamari-clients (https://github.com/ceph/calamari-clients/pull/37). It adds a SUSE-specific spec file, and expects this spec file and a tarball of the source tree to be uploaded to build.opensuse.org. See, for example, the package at https://build.opensuse.org/package/show/home:tserong:calamari/calamari-server

The SUSE build tries as much as possible to install globally following FHS paths (/var/lib/calamari, /var/lib/cthulhu, /usr/lib/python*/site_packages, etc.). This is handled by the `build-unpacked` and `install-suse` Makefile targets, the former of which should be generic enough to be usable on other distros too, if this approach is deemed generally desirable.

I've added a systemd service file for cthulhu, so it should be possible to do away with supervisord, at least on systemd distros.

There are still some things installed to /opt/calamari (everything I've listed it http://lists.ceph.com/pipermail/ceph-calamari-ceph.com/2014-July/000174.html) - I have *not* included my changes to install this stuff to /etc in this pull request, as that would either require a bunch of conditionals, or would break other non-SUSE builds, both of which I assume are undesirable ;-)

There are still some rough edges, but IMO this is in about the right shape to give a generally usable build on SUSE, without breaking or disrupting builds for anyone else.