Add git-review configuration to repository

Add .gitreview to enable the use of the git-review plugin to interact
with Gerrit. Documentation on this plugin can be found at:

  https://github.com/openstack-infra/git-review

Change-Id: I8240a5baf7e1171b932896a6615131453b55adad
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-on: https://git.eclipse.org/r/69173
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Jonathan Rajotte Julien <jonathan.rajotte-julien@efficios.com>
Reviewed-by: Alexandre Montplaisir <alexmonthy@efficios.com>
Tested-by: Alexandre Montplaisir <alexmonthy@efficios.com>