Adding support for decommissioning

The pluggable hardware manager should be able be used for decommissioning,
such as erasing disks, updating firmwares, changing BIOS settings, and
anything else specific hardware needs. This works with the agent driver
to store state in Ironic and request out of band reboots (which may be
required to make BIOS/firmware updates work).

Change-Id: Ia42a8e75d2b8887b2351de97c2137fe21a7f4041
(cherry picked from commit bdbb882037079ceaae1c73f0e1a0bb20c3d49373)
Add versioning to Agent decommission

As the agent will likely be rebooting while decommissioning (to apply BIOS/
firmware upgrades), it is possible the version of the agent will change
between boots. Including a version string in the Hardware Manager allows
the Hardware Manager builder to bump versions for any breaking changes.
I recommend that the entire decommission process be restarted if there
is a version mismatch, but that will be up to individual drivers to
implement.

This change also adds a new return value for Agent REST commands called
'DECOM_VERSION_MISMATCH' that will signal no command was run, and
Ironic should update its stored value. A 'hardware_manager_version'
will be returned with AsyncCommandResult, and should be set in the
Ironic driver_info field and sent with any decommission command.

Change-Id: I2ae0e93573e0348f023aa124a07bb16921b5c53e
(cherry picked from commit 9131b860ce8f3318e0f8a50f8771fed944ae9bb3)
Improve Disk Detection

The previous implementation of list_block_devices used blockdev,
which would list partitions, software RAID and other devices as block devices.
By switching to lsblk, the agent can filter down to only physical block
devices, which is all the agent cares about for any of its operations.

This change adds two new fields to the BlockDevice class: model, a string of
the block devices reported model, and rotational, a boolean representing a
spinning disk (True) or a solid state disk (False). This data can be useful
for vendor hardware managers.

Change-Id: I385c3bb378c2c49385bca14a1d7efa074933becf
Closes-Bug: 1344351
(cherry picked from commit 83782018f73266d52e5c3fab6e82f3d3257fb94d)

Conflicts:
	ironic_python_agent/errors.py