Ports image_size extension to v3 API

This merges the functionality from the v2 image_size functionality into
the images extension (which is no longer core in v3)

Partially implements blueprint nova-v3-api

Change-Id: I577907e671d18712893afcb5477fbd2aa6031956
PowerVM resize and migrate test cases

Resize and migrate functionality for the PowerVM driver
was landed without tests.

Fixes bug 1133058

Co-authored-by: Matt Riedemann <mriedem@us.ibm.com>
Change-Id: I9b46f092ebaab630fe80e0306ea32bda5a4c1d2f
Sync install_venv_common from oslo

Change-Id: Ib85067b1eb22638fddb8c70c468bfc458c4524d9
Merge "Ports image_size extension to v3 API"
Merge "Sync install_venv_common from oslo"
Merge "PowerVM resize and migrate test cases"