Switch server tests to use .ini

Reviewed By: @paulbiss

Differential Revision: D1649792

Signature: t1:1649792:1414694605:e0d2bc89d33f19f5e612e5bc5a5a9715c55deaaa
Disallow mixed enums

Summary: If you have a mixed enum with a falsey value, then a `switch`
on that enum can lead to very unexpected results, since `switch` uses
`==` equality. This form of enum is of questionable use anyways, so
let's just disallow it.

Reviewed By: @elgenie

Differential Revision: D1646639