Add quantum_available config option

This lets us globally enable or disable tests that require quantum.

Change-Id: Id0452e98c6b21dcae92b79b545728e8444c474a3
Add tests for nova's os-attach-interfaces extension

Note that this requires quantum networking on the target machine.

Change-Id: Ieb210e107c28e9dc83884415b28cfefdeaf0f6e2
Merge "Add quantum_available config option"
Merge "Add tests for nova's os-attach-interfaces extension"