test: Add a blur test case

* Derived from pixman-rotate.c test case.
* Added shadow functionality to blur test case
* Draws a ring to test blur rendering
  Design lifted from Henry Song's cairo-glx-shadow-ring.c example.

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
test: Use current output as reference image for blur

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>