VMware: factor out the management of unit numbers

[Radoslav Gerganov]

Virtual devices need a unit number when they are attached to a controller. We cannot have two devices on the same controller with the same unit number.

Currently, the selection of unit numbers is spread all over the driver code, leaking to high-level functions like spawn() and rescue(). We need to factor this out into helper functions which take care of choosing a proper unit number and creating additional controllers if needed.

High-level functions need to communicate only the intent like 'attach CDROM' or 'attach disk' and shouldn't bother with details like unit numbers.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/66523

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/66523
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=ecdc5728ca849fd19d01c2a69cf07bf0989e8567
Submitter: Jenkins
Branch: master

commit ecdc5728ca849fd19d01c2a69cf07bf0989e8567
Author: Radoslav Gerganov <email address hidden>
Date: Tue Jan 14 11:02:07 2014 +0200

    VMware: factor out management of controller keys and unit numbers

    This patch encapsulates the allocation of controller key and unit
    number for a new virtual disk/CDROM into utility function.
    This way high-level methods like spawn, rescue, etc. don't have
    to deal with implementation details like the above and the
    algorithm for allocating controller_key and unit_number is
    clearly defined and can be easily reused.

    Change-Id: Ia6d5db5d5c5fa25f680eae82892dcb9b2be864fa
    Closes-Bug: #1259981