Add large_ops scenario test

Try spinning up a specific number of instances (set via config) by using
the min_instances option. And make sure all instances go to active
state. Note since the number of instances a cloud can handle is cloud
specific this test is disabled by default.

This can be used in Devstack by using the 'VIRT_DRIVER=fake' option in
devstack.

Change-Id: I30c7d7d113053b47d6dffa6295ad6068810cad32
4 files changed