Check for sudo_rules before text.append state.

Since ebe5198f, if a user's pillar dict didn't contain sudo_rules, a broken
file.append state would be rendered (since some text is required). With
this patch, the file is still created/managed by the previous state, but
will be empty by default if created fresh. This seems a more sensible
default than assuming a default sudoer policy.

Further, since the first word on each rule line should be the user's
name, that is now assumed.
Merge pull request #18 from hipikat/fix-sudo_rules

Check for sudo_rules before text.append state.