Image properties in scenario tests

Some images require additional properties.
This change adds dictionary option "img_properties"
to the "scenario" config section.
For example, to work with Parallels Containers, specify vm_mode:
img_properties = vm_mode:exe

By occasion, we fix handling properties in _image_create in scenario/manager.py:
disk_format is an x-image-meta-* option, and kernel_id, ramdisk_id are properties.

Change-Id: I2d3714eb899faad67a867a630c1d72d1fd8ee74f
3 files changed