Ability to contribute functional tests

Currently addon testing is done by:

• building the addon
• building a Marketplace package for the addon
• running a dedicated job on QA which will:
  • prepare a Nuxeo server and deploy the addon MP inside
  • start the server
  • run the addon's functional tests
  • stop the server

All this, multiplied by the number of addons, takes too much time and requires a lot of configuration.

A solution would be:

• building the addon
• building a Marketplace package for the addon
• running the Nuxeo generic functional tests which will:
  • prepare a Nuxeo server and add inside (instead of deploy) all the addons MPs to be tested
  • start the server
  • run the generic functional tests
  • run all the addons contributed functional tests ; per addon the functional tests have to install the relevant MP at setup() and uninstall at tearDown()
  • stop the server

At long term, there would be no more "generic functional tests":

• every module (addon or default module) would embed its functional tests,
• every Marketplace package (addon MP or default MP such as DM, DAM, ...) would deploy the testing JARs in the server (for instance in `"$NUXEO_HOME/tests"` or `"$NUXEO_HOME/sdk/tests"`),

That will only work with hot-reload-able packages, but at mid or long term, (almost) all packages should be hot-reload-able.