New formats added to Draw Buffers Indexed Tests

New formats added to Draw Buffers Indexed Tests

- Add function getFloatULPThreshold to compute the threshold
  for float formats.
- Context argument added in the function getRandomFormat
  to pick a format acording to the context version.
- The formats GL_RGB16F, GL_RGBA16F, GL_R32F, GL_RG32F,
  GL_RGBA32F, and GL_R11F_G11F_B10F have been added to
  the array glFormat wich will be chosen randomly.
- The suffix "_KHR" was removed from the name of the
  advanced blend equations.
- Validate to exclude and throw a NotSupportedError if
  the contex isn't version 3.2 or the extensions
  GL_EXT_draw_buffers_indexed and GL_KHR_blend_equation_advanced
  are not supported.

Change-Id: I0d7f0a295049e5e715b3854a9df15662a6005861