Fix to create an image with given  min_ram value.

Currently the create_image() method creates an image by setting
'min_ram' value to zero.When create_image() is asked to create
an image with different 'min_ram' value say '40' it ignores this
and still creates the image with 'min_ram' value set to zero.
Also adding a new test named "test_register_image_with_min_ram"
just to make sure that create_image() indeed creates an image
with the given 'min_ram' value.
This fixes Bug #1166675

Change-Id: Ie90ec93c04b538dc9cb991e6836727a507c9eb00
Merge "Fix to create an image with given  min_ram value."