Return empty list when listing servers with bad status value

API indicates the status parameter is a string, hence status=BALONEY is a valid
filter that should return zero records since no records match that status. The
return should be an empty list and 200 OK.

Fixes bug 1061712

Change-Id: If796110a18dd75ab5c5d4ba41e9c3b58180341f8
(cherry picked from commit e142d21b47e8895a013c468936e69ba0e7e66041)
Merge "Return empty list when listing servers with bad status value" into stable/folsom