nGraph: fix TopK output shape inference (#2967)

nGraph: fix TopK output shape inference (#2967)

* nGraph: Fix TopK output shape inference

* nGraph: Correct TopK output shape inference

TopK lower bound of output shape at the axis was mistakenly calculated
basing on max_lenght instead of min_lenght.

* nGraph: Correct TopK output shape inference

* nGraph: Correct TopK type prop test

The topk_negative_axis_support type properties test was comparing
incompatible variables carrying the same value. So it was passing ok.

* nGraph: Add TopK type prop test

* nGraph: Fix code style

* nGraph: Follow review guidelines

Improve variables meaning.
Enforce rigid test pass condition.

* nGraph: Remove magic numbers