Generic matrix testing -- left and right kernel

[jasongrout]

This patch implements generic testing for left and right kernels. It exposes lots of bugs.

CC: @rbeezer

Component: linear algebra

Author: Jason Grout

Issue created by migration from https://trac.sagemath.org/ticket/7991

[jasongrout]

Attachment: trac-7991-generic-kernel-testing.patch.gz