omego db upgrade

Originally I used the `psycopg2` python module to connect to Postgres (https://github.com/manics/omero-setup/compare/f42ba2d42f092e3e78930248a295285965816785), but this is an additional dependency which may require the postgres-devel package and a compiler. 8195422 changes this to use the `psql` binary instead. The `PGPASSWORD` envvar is used internally to pass the password to `psql`. If DB backups are implemented the `pg_dump` binary will need to be run anyway.

* `omego db upgrade --dbhost host --dbname name --dbuser user --dbpass pass --serverdir path/to/server`
* `omego db init --dbhost host --dbname name --dbuser user --dbpass pass --serverdir path/to/server`
* `omego upgrade --dbhost host --dbname name --dbuser user --dbpass pass  --upgradedb`

`OMERO4.4` to `OMERO5.0` and `OMERO5.0` to `OMERO5.1DEV` should work.

Note credentials aren't read from `config.xml` so if you've got multiple DBs ensure you pass the connection details.

Current issues:
- [ ] Credentials. Currently passed on the command line, should they be read from `etc/config.xml`, or by calling `bin/omero config get omero.db.xxx`
- [ ] Initialisation. If this is a new DB then perhaps it makes sense to take the credentials from the command line and use those to set the omero config, perhaps along with other server initialisation tasks.
- [ ] Tests. Currently there are none.
- [ ] Should this go in `omero db` instead? Or will we end up tying ourselves in knots?
- [ ] `omego db upgrade --dry-run` tells you if an upgrade would be performed, `omego upgrade --upgradedb --dry-run` doesn't
- [ ] Travis. It should be failing without this db upgrade, it's not.