cl: Fix char/short test names

Several tests still had '%' in the test names, which Tom made an illegal
character a ways back.

Reviewed-by: Tom Stellard <thomas.stellard at amd.com>
cl: Add test of get_global_size(dim)

Based on the test cases for get_global_id

Reviewed-by: Tom Stellard <thomas.stellard at amd.com>
piglit-summary.py: remove unused imports

As suggested by Dylan Baker.