libvirt: introduce new 'Host' class to manage the connection

Move all the code related to obtaining a new libvirt connection
out into a new 'Host' class. This covers the initial connection
attempt, testing of the connection, handling of connection close
events and handling of lifecycle events.

The appropriate tests are also moved out into a new HostTestCase
class

Blueprint: libvirt-driver-class-refactor
Change-Id: I64e84c4ed7b275632ef2ce3fa6e4be4c0ee8235a
Hyper-V: Adds HostOps unit tests

The Hyper-V driver oldest tests (test_hypervapi.py) are proving hard to
maintain.

The tests in test_hypervapi.py in particular can also be refactored and
split in separate TestCases, one of each *ops module.

This commit refactors the HostOps test cases.

Co-Authored-By: Robert Tingirica <rtingirica@cloudbasesolutions.com>

Partially implements: blueprint hyper-v-test-refactoring

Change-Id: I2f20401ed8c01c08d2fecab9356b70ee58b3e8fa
Port virtual-interfaces plugin to v2.1(v3) API

Ports virtual-interfaces extension and adapts it to the
v2.1/v3 API framework. API behaviour is identical.

- unittest code modified to share testing with both v2/v2.1
- Adds expected error decorators for API methods

Partially implements blueprint v2-on-v3-api

Change-Id: Ic25ae83ecfaaa461b6ddd044e04af844d02dd6b7
Code cleanup: quota limit validation

In the quota limit validation, the conditional expressions are
difficult to understand because -1 which means an unlimited value is
compared directly.

By converting -1 to infinity, the validation can be implemented with
simple numeric comparisons. It makes code maintenance much easier.

Change-Id: I74650cba121734a14d31b76607adea004804c815
Imported Translations from Transifex

For more information about this automatic import see:
https://wiki.openstack.org/wiki/Translations/Infrastructure

Change-Id: I3823ea46b26b921642b373b1495ffb3a448f121f
Merge "Port virtual-interfaces plugin to v2.1(v3) API"
Merge "Code cleanup: quota limit validation"
Merge "Imported Translations from Transifex"
Merge "Hyper-V: Adds HostOps unit tests"
Merge "libvirt: introduce new 'Host' class to manage the connection"