Upgrading HaaS

This file describes the procedure for upgrading HaaS to a new version.

Read the release notes, as they may contain version-specific information.
Stop the HaaS services (webserver and HaaS network daemon). For exmaple:
```
$ systemctl stop httpd
$ systemctl stop haas_network
```

Download and install the new version of HaaS:

$ git clone https://github.com/cci-moc/haas
$ python setup.py install

Upgrade the database:
```
$ haas-admin db upgrade heads
```
heads indicates that HaaS core and all extensions should be upgraded together. This is the only workflow we support, but the curious can read the (developer-oriented) alembic documentation for more information:
- https://alembic.readthedocs.org/en/latest/
- https://alembic.readthedocs.org/en/latest/branches.html
If additional extensions have been added to haas.cfg, re-run haas-admin db create, which will create any tables needed by those extensions.

Note that removing extensions is not currently supported.

Restart the HaaS services. e.g.:

$ systemctl start httpd
$ systemctl start haas_network

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