Write and test different update scenarios

Typically: upgrade available, upgrade / downgrade needed, up-to-date.

This task depends on NXDRIVE-4, and will probably invoke the commandline from a shell (or Python?) script, something like:

• Activate virtualenv
• Install requirements with pip
• Start mock update site
• Set current version to a given value by writing in nuxeo-drive-client/nxdrive/_init_.py
• Freeze application with Esky
• Package frozen app into a MSI / DMG
• Install package
• Bind server with ndrive bind-server (requires a running Nuxeo instance)
• Fetch update information and check update status with something like ndrive update-status (should be "up_to_date")
• Set new version to a given value by writing in nuxeo-drive-client/nxdrive/_init_.py
• Freeze application with Esky
• Package frozen app into a MSI / DMG
• Deploy package to the mock update site
• Fetch update information and check update status (should be "upgrade_available")
• Process an update action, for instance ndrive update
• Check the current version has been upgraded with ndrive --version

Note that part of this process will be used in Jenkins jobs to build, test and deploy the binary packages.