remove some unused code in nova image tests

this removes some unused alt_client and images_id in the nova image
tests.

Change-Id: Ied9f098be9bbbc845ad07a40bfedf2dab9b9eceb
Introduce T106 rule for vi modelines

We don't need to have the vi modelines in each source file anymore.
We've already fixed them several times.
 https://review.openstack.org/#/c/66507/
 https://review.openstack.org/#/c/68552/
 https://review.openstack.org/#/c/69318/
 https://review.openstack.org/#/c/70133/
However, newly some files still have it in its header. So we should
check it automatically with our HACKING rule.
This commit introduces T106 rule for that.

Note: This code is copied from Nova's hacking rule.
   Change-Id: I347307a5145b2760c69085b6ca850d6a9137ffc6

Change-Id: I5c94ef041a39c2377ba6321ace8934f324287bcf
Closes-Bug: #1229324
Merge "remove some unused code in nova image tests"
Merge "Introduce T106 rule for vi modelines"