[tests] Cleanup asserts

Use nose.tools assert everywhere
2 jobs for 24_assert_cleanup in 11 minutes and 9 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Build
passed #164808
docker
build_linux_36

00:04:44

73.0%
passed #164809
macosx
build_macosx_36

00:11:09

73.0%