Move nova-network tasks to tasks.network.nova subpackage

Also add plugin layer to tasks.network
Add Neutron client to Cloud objects
Add setup implementations for network manager plugin

Two plugins supported:

* FlatDHCP
* VLAN

Setup selects plugin from configuration and executes appropriate setup_network
function.
initial neutron supporting commit
Neutron network migration tasks
pep8 fixes
fixed multiple pep8 warnings and typos
Fixed multiple typos
Added neutron exception
Fixed create_network call
create_subnet->create_network
Fixed create_subnet implementation
Pass plugin configuration to setup function

Pass PLUGINS configuration dict to setup function to support networks
setup in environments with different network managers.
Pass events handler to setup_networks functions

This is required to emit setup-related events during reset.
Remove pip cache configuration from tox.ini
Merge remote-tracking branch 'origin/master' into network-migration-tasks
Network dict generator plugin implementations

Two network managers are supported:

* "FlatDHCP" for nova-network
* "VLAN" for nova-network

Selection controlled by the same parameter as setup (PLUGINS:network_manager).
Use tempfile for caching test image
Random suffixes for test resources in setup

This is needed to avoid conflicts in case of faults during reset. Resources
created by subsequent setups will not conflict with resources from previous
setup runs.
Correct handling of lists of ip addresses

If Nova API returns a list of ip addresses in 'cidr' field of network dict, use
netaddr.IPSet to create range from the list. Otherwise, pass the list 'as is'.