Add api extension to get and reset password

Password is stored in system_instance_metadata as four items with the
keys 'password_0' through 'password_3'. The extension adds a resource
endpoint with two methods:

GET v2/servers/<uuid>/os-server-password  # get_password
DELETE v2/servers/<uuid>/os-server-password # reset_password

get_password retuns:

JSON: {"password": "xxx"}
XML: <?xml version='1.0' encoding='UTF-8'?><password>xxx</password>

Note that this is intended to be an encrypted password set by the
guest. Includes api tests for json and xml. Also includes api samples.

Part of blueprint get-password

Change-Id: I6c03f9c3bc8a2c70403bbb3e57917ab9522d75bd
Remove unused osapi_path option

This has been unused since deprecated auth was removed. It looks like
we intended to remove this in commit ea06eff7.

Change-Id: I7a5868c42300ba92d5c8f528a447cfe3fbace297
Fix baremetal VIFDriver

Commit Id287f7e661 removed the nova/virt/vif.py file and the VIFDriver
base class, and erroneously stated in its commit message that baremetal
driver did not use it. This patch repeats the work of that earlier patch
by removing the import of nova.virt.vif from baremetal/vif_driver.py.

blueprint general-bare-metal-provisioning-framework

Change-Id: Ifac9510a72a028dc5d3574148f3c4a6410b1d249
Refresh instance metadata in-place

For some reason that isn't entirely clear to me, the attempt to update
instance metadata in _instance_update() results in a stale sqlalchemy
object state. This is a similar issue to the one fixed in commit:

  9fdf7552779d518af9cda4e366bf81fddb0cb6f2

For some reason, session.refresh() doesn't work for instance['metadata']
in the same way, which also raises suspicion that perhaps it's not the
right fix for system_metadata either.

This patch adds an _instance_update_metadata_in_place() method that
updates the actual instance['metadata'] list _and_ the database,
mirroring the high-level behavior of instance_metadata_update(), but
without requiring us to refresh or re-fetch the metadata or the
whole instance (as a workaround).

Fixes bug 1096653

Change-Id: Ic5a205631b1b7dce3744960ed4201dcc7b4b2ae6
Merge "Refresh instance metadata in-place"
Merge "Add api extension to get and reset password"
Merge "Remove unused osapi_path option"
Merge "Fix baremetal VIFDriver"