Return 404 for empty parameters in URLs

For 2nd level controllers like nameservers or recordsets, pecan does not
correctly check for empty UUIDs. Now we handle those cases and return
a 404 for URLs like /v2/zones/nameservers or v2/zones/recordsets

Change-Id: I171fee12816399a9056e6688677d48f97a5281e3
Closes-Bug: 1288830
Merge "Return 404 for empty parameters in URLs"