[Piglit] Fix bad behavior in GleanTest

[Dylan Baker]

GleanTest has a pretty bad behavioral problem that was exposed by the
conversion from execfile() to importing piglit tests. This problem is
related to GleanTest's unique globalParams class attribute, which is
used to add arguments to all glean tests; in this case it is used to set
the --quick option in quick.py. The problem is that this parameter is
add by the constructor to a static attribute at instance initialization,
so setting or changing that parameter only applies to new GleanTest
instances. This is not clear or straightforward behavior.

Jose spotted this problem and implemented a workaround quickly, but this
behavior is bad and should be properly fixed to prevent future
breakages.

Patch 1 adds a test to demonstrate the problem, and to show that the
solution fixes it.

Patch 2 fixes the problem, using getters and setters to apply the
globalParams dynamically rather than statically

Patch 3 reverts the workaround, since the problem is now fixed, and the
workaround is not pep8 compliant