Workloads configuration support in setup

Configuration file allows to create test workloads in source cloud, described by
YaML formatted dictionary. Tenant workload type is supported. Tenant workload
dict might include 'volumes' section. Volumes defined there will be created by
setup function.
Volumes attachment to servers can be defined in 'workloads' config by adding
'volumes' list to 'server' definition.
Example:
workloads:
    tenants:
        name: pumphouse-test-1
        ...
        volumes:
            - &volume1
                size:           1
                display_name:   pumphouse-test-vol-1
        servers:
            -
                name:           pumphouse-test-server-1
                volumes:
                    - << *volume-1