[Piglit] faster piglit start-up

[Chad Versace]

On Wed 12 Apr 2017, Eric Anholt wrote:

> For a solution to the startup time, I wish we would just build our whole
> test list using filesystem walks or whatever at piglit build time,
> instead of executing python to build the test list per piglit run.

A nice benefit of building the test list just once, at buildtime, is
that it then becomes possible to teach the shell to tab-complete
`piglit run` with testnames.

FWIW, that's what the Crucible testsuite does. All the testnames are
compiled into the crucible executable at linktime.

Here's Crucible's bash-completion file.
https://cgit.freedesktop.org/mesa/crucible/tree/misc/crucible-completion.bash?id=3c3eb6175af13fb2efe2563cbc419d216b3291b9