Add network support to the accounts providers

This commits adds support for specifying the network to use with a
user/tenant into the accounts.yaml file. You can only specify a single
network which will be the network used for all that requires a
pre-existing network. This also means regardless of which cred provider
is configured the fixed_network can assume a TestResource object will
be returned from a get_creds call. As part of this change a common
method to return the full network dict from a just a network name is
abstracted out into tempest.common.fixed_network module since this
same method is needed to have the accounts file provide a network by
name.

Partially-implements: bp test-accounts-continued
Change-Id: I6f5ac1239d18f2935847b385a08de608f40fdda5
5 files changed