fixup! glsl_parser_test.py: Remove standalone functionality.
exectest.py: Merge GleanTest into exectest

It doesn't really make sense to have a dozen test modules.
exectest.py: Code cleanup and refactoring

Cleans up and refactor some code, mostly to meet style guidelines or
remove deprecated functions like filter() and map(). There are also a
few cases or replacing small loops with list comprehensions.
exectest.py: Move Test baseclass from core

Since Test is only used as a base class by ExecTest it makes sense to
put both of them in the same module.
exectest.py: move testBinDir from core to exectest

Since this exists mainly to be used by test classes it should live in
their module.
Remove unused shell script

This is just some unused legacy code I found while greping through the
tree.
exectest.py merge shader_test

Shader tests are just a wrapper for PlainExecTest, so lets put them in
the same module.
exectest.py: merge glsl_parser_test

This is also just a wrapper for PlainExecTest, so just merge it into
exectest.
exectest.py: Refactor Test, ExecTest and PlainExecTest

Piglit has this strange three class inheritance scheme, where Test and
ExecTest serve purely as abstract base classes, however no test inherits
directly from Test, they all inherit from ExecTest.

What this patch does is merge Test and ExecTest into a single abstract
base class, Test, then renames PlainExecTest to PiglitTest (since it's
all about running native piglit tests), it then refactors other tests to
inherit from Test instead of ExecTest.
Replace testBinDir with pep8 compliant TEST_BIN_DIR
googletest.py: Refactor several test modules into one

Previously there was a module for gtest (short for googletest), and one
for opencv. Since there might be further use for googletest, but
probably not any additional children of opencv it makes sense to
refactor this to be about googletest.