Some tests take too much time to run

Some tests are taking a very long time for a unittest. The worst offenders lately are:

    20.60 test_allocate_and_deallocate_instance_static (nova.tests.test_quantum.QuantumNovaIPAMTestCase)
    19.92 test_allocate_and_deallocate_instance_dynamic (nova.tests.test_quantum.QuantumNovaIPAMTestCase)
    19.12 test_create_and_delete_nets (nova.tests.test_quantum.QuantumNovaIPAMTestCase)

But other tests taking more than 3-4 seconds are also a bit suspicious. This may not be that important during local development when one test module can be selected (although CloudTestCase is slow too), but whenever some code is completed, it needs full retesting and possible corrections on top of current master branch.

It would be good if some "red" times went away.