Add boot_from_volume benchmark

Added boot_server_from_volume_and_delete and
boot_server_from_volume benchmarks. Config example is below.

{
    "NovaServers.boot_server_from_volume_and_delete": [
        {
            "args": {"flavor_id": 1,
                     "image_id": "cd6f34f4-b205-48b2-939b-0e80b8a94928",
                     "volume_size": 10},
            "execution": "continuous",
            "config": {"times": 10, "active_users": 2, "tenants": 3,
                       "users_per_tenant": 2}
        }
    ]
}

Change-Id: Iba5997fa336d3a6d1686137ab70a52a5087180f2
Merge "Add boot_from_volume benchmark"