Adding a .gitreview file

This enables easy use of the git review command documented on the wiki here:
https://wiki.opendaylight.org/view/Git-review_Workflow

Change-Id: I2c7373cae2d56e07a5a6da2930a2c471f469c5cd
Signed-off-by: Colin Dixon <colin@colindixon.com>
Merge "Adding a .gitreview file"