Adding new common image properties

Revised schema and glance sphinx docs, renamed 'os_arch' to
'architecture' for backwards compatibility, renamed 'os_shortid'
to 'os_libosinfo_shortid'.

Partially implements blueprint glance-common-image-properties

Change-Id: I23d8ba82015f1f53bff65b4fa08463d905eeadd8
Sync latest install_venv_common.py

Syncs:

c78b2ab Avoid using cfg in install_venv_common

So that people don't need oslo-config installed to run install_venv

Fixes bug 1130853

Change-Id: I9dfc8d8417455ff22a0d0e911c762983952c75ee
Merge "Sync latest install_venv_common.py"