Test EXT_shader_group_vote using variables

Test EXT_shader_group_vote using variables

Current tests call shader group functions passing directly True/False
values. This change adds test that verifies new functions using
variables.
This change also reduces workgroup size for ES as all tests were
previously using workgroup size that was greater than the minimum
required.

Components: OpenGL

VK-GL-CTS issue: 693

Affects:
KHR-GL45.shader_group_vote.*
KHR-GLES31.core.shader_group_vote.*

Change-Id: Icbb5c278c65edd04fe339e31934df7624834c439