Add new resource access flags to system metadata mocks

[selimnairb]

In addition to "public": true the REST API now returns the following access flags to system metadata for a resource:

"discoverable": true,
"shareable": true,
"immutable": false,
"published": false,

The client doesn't currently need to reference these flags, but the mocks should be updated so that our tests don't drift from the current message format.