Hyper-V: Skip logging out in-use targets

As most of the Cinder volume drivers that use iSCSI export one LUN
per iSCSI target, the Hyper-V driver was logging out the according
target each time a volume was disconnected.

This causes issues with some volume drivers that use multiple LUNs
per iSCSI target and may disconnect in-use targets.

This patch fixes the issue by checking if there are other LUNs
being used, disconnecting the iSCSI targets otherwise.

Change-Id: Ida08e7129a7b7940ddea488488cccc7571a43b76
Closes-Bug: #1372815
Updated from global requirements

Change-Id: I0f3cb3023952f889650c3ebbd0fb6aee5861898d
Merge "Hyper-V: Skip logging out in-use targets"
Merge "Updated from global requirements"
Add tox -e functional

Provide a tox -e functional stub, as a place for functional tests to
migrate to. This will allow us to write a zuul test configuration for this
environment.

Part of bp:functional-tests-for-nova

Change-Id: I8a1107beab151f9bf574cfbae1d4dc18400fd74e
move all tests to nova/tests/unit

As part of the split of functional and unit tests we need to isolate
the unit tests into a separate directory for having multiple test
targets in a sane way.

Part of bp:functional-tests-for-nova

Change-Id: Id42ba373c1bda6a312b673ab2b489ca56da8c628