I ran across this when trying to deploy the site today. Rather than update pom.xml with my username, I set a global username in my subversion config. I think I could have also set a global password there, but I used Olaf's method of passing in my password at build time.
I don't have access to update the wiki just yet, but in case someone else finds this jira from the Deploying Bigtop's Apache Website page, here's what I added at the end of ~/.subversion/servers:
username = kwmonroe
With that in place, this worked for me:
mvn -Dpassword=xxxxxx site-deploy