When running in devstack, you need to set the SERVICE_VARIANT so that
assets.py knows what environment file to use.  Recall that in devstack
we have all our settings in ../lms.env.json, not just ../env.json.  So
you need to run like this:

    SERVICE_VARIANT=lms paver lms --settings=devstack

Previously you'd get this error:

    Warning: could not find environment JSON file at 'lms.env.json'

Note there is no path on the file, that's the bug.  By making
self.REPO_ROOT absolute, we can walk up the tree and correctly find
the file, which is /edx/app/edxapp/lms.env.json fwiw.

and print errors and warnings to sys.stderr

Simpler and clearer

This reverts commit 544616be.

Restore reverted changes from paver part 1

This reverts commit df2e410f.

Deprecated rake functions issue a warning and then call paver
replacements

Bring Paver commands up to date with master for servers, assets, and docs.
Revert deprecation of quality, tests, and i18n for a future pull request.
Deprecate workspace migration