Improve and fix quad randomization in vertex array test

Improve and fix quad randomization in vertex array test

Minimum quad size for fixed point format was larger
than the maximum value range, causing only extremely
large quads to be used. Also the quad randomization
relied on a loop with fixed number of attempts to
produce proper quads. Now the randomization ranges
are selected so that the quads can be accepted without
multiple attempts.

VK-GL-CTS Issue: 3376

Affects:

dEQP-GLES3.functional.vertex_arrays.*

Components: OpenGL ES
Change-Id: I648f2218aa9b661969c7b78c2f81b5e120ae9275