added users and a logo

Adds a horizon user to the mix. This makes it so horizon will work
in ubuntu and cent/rhel without issues.
All horizon files will now be owned by the horizon user.
added better user create params

adds a not_if statement which allows us to create a horizon user
if the horizon user is not found on the system. This is useful when
the package does not create this user.
Merge pull request #137 from cloudnull/master

Update for users and logos