ci: Add make check-kernel to GitHub actions ci.

This patch adds 'make check-kernel' to the GitHub actions ci.
However, to do this, some additional changes were needed. First,
some of the missing test and package dependencies had to be added.
Finally, we added an option to the GitHub run matrix that allows
the tests to be split up, to avoid lengthy single test runs.

Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Simon Horman <horms@ovn.org>

python/test_requirements.txt

@@ -1,3 +1,5 @@
-pytest
 netaddr
+pyftpdlib
 pyparsing
+pytest
+tftpy