Splits service_instance module from generic driver

This module may be used by arbitrary share driver
if it uses multitenancy approach of generic driver.
Methods, responsible for managing nova instances
and setting up network connectivity were taken out
from generic driver to this module.

Implements: bp generic-driver-modularity
Change-Id: Iedf5eee4db716fd0c75ac3b49af975e0e2284ab2
Merge "Splits service_instance module from generic driver"