deqp: Add test profile for external dEQP-GLES3 tests (v4)

Google opensourced the drawElements Quality Product Testsuite (dEQP) as
part of the Android Lollipop release. It's git repo lives in the Android
tree at [https://android.googlesource.com/platform/external/deqp/].

This patch adds a new module, deqp_gles3.py, that runs the dEQP-GLES3
tests.  It queries the 'deqp-gles3' executable at runtime for the list
of testcases.  The module attempts queries the 'deqp-gles3' executable
only if the environment variable PIGLIT_DEQP_GLES3_EXE or the
piglit.conf option deqp-gles3.exe is set.

Why do we need to use Pigit as the testrunner for dEQP? (After all, dEQP has
its own testrunner). Because dEQP runs all tests in a single process. If test
17530 of 55409 crashes, then the dEQP testrunner crashes and the remaining
tests never run. Piglit doesn't suffer from that problem, because it runs each
test as a separate process.

Tested on Intel Ivybridge by running the command
    piglit run -t dEQP-GLES3/info/vendor \
      tests/deqp_gles3.py tests/quick.py results
with and without PIGLIT_DEQP_GLES3_EXE set and with and without
piglit.conf:deqp-gles.exe set. Also tested with various combinations of
valid and invalid values for PIGLIT_DEQP_GLES_EXTRA_ARGS and
piglit.conf:deqp-gles.extra_args.

Cc: Dylan Baker <dylanx.c.baker@intel.com>
Cc: Michael W Mason <michael.w.mason@intel.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>