Remove tempest deprecated img_dir option

Tempest option scenario.img_dir has been deprecated more than 4 years, it's
time to remove it from devstack.
img_file option should contain the full path to the image.
This patch removes setting of img_dir option and makes img_file
one contain the full path of an image.

Change-Id: I71102095f3603915f0bc7d21f2e18c4eac4e95ec
Depends-On: https://review.opendev.org/#/c/710996/
Related-Bug: #1393881
1 file changed