Return tags field in create_network
Return tags field in create_network

1. What is the problem
OpenStack client will read "tags" field for network creation command,
but create_network in central plugin doesn't return this field.

2. What is the solution for the problem
Fill "tags" field in the returned body

3. What features need to be implemented to the Tricircle to
realize the solution
N/A

Change-Id: I2537bcc9e61dc95a6cfb9e2853c8a2ea32310eb2
Closes-Bug: #1715103

stackforge/tricircle,stackforge/tricircle,openstack/tricircle,openstack/tricircle