Tab cleanup in site.pp. Also fix vim modeline

Some tabs had crawled into this file, probably a result of two
conflicting modeline rules, one doing expandtab and one negating it
Replace the tabs with 4 chars and set a reasonable vim modeline

Change-Id: I41f10e0e9c50c6f6facb5d356c3f0bd52d36fba8
Merge "Tab cleanup in site.pp. Also fix vim modeline" into production