dim: Ensure a branch doesn't exist before creating it

Check the remote for the branch before creating it. Seems like this is
a noop if it does exist, aside from creating duplicate entries in the
integration config.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

dim

@@ -1215,6 +1215,10 @@ function dim_create_branch
 	fi
 
 	remote=$(repo_to_remote $repo)
+	if [[ $(git branch -r | grep "$remote/$branch") ]]; then
+		echoerr "$branch already exists on $remote"
+		return 1
+	fi
 
 	$DRY git branch $branch $start
 	git push $DRY_RUN $remote +$branch --set-upstream