Update CREDITS list

Signed-off-by: Mike McClurg <mike.mcclurg@citrix.com>
Merge branch 'master' of github.com:xen-org/xen-api into credits
Update CREDITS with git log --format='%aN' | sort -u

Signed-off-by: Mike McClurg <mike.mcclurg@citrix.com>
Merge pull request #1290 from mcclurmc/credits

Update CREDITS list