Add networks property to OS::Trove::Instance

Trove client recently added possibility to provide NICS while creating
Trove instances, which is required in presence of multiple Neutron
networks. This patch adds such property to OS::Trove::Instance resource,
allowing usage of this new feature in Heat.

Closes-Bug: #1312474
Change-Id: Ie691702bb2e2537397ed7ae657eb8d088424d890
Merge "Add networks property to OS::Trove::Instance"