fixup! Incorporate review feedback from mtrmac

- Got TLS registry working, and test enabled. The trick was to
  copy the .crt file to a separate directory *without* the .key

- auth test - set up a private XDG_RUNTIME_DIR, in case tests
  are being run by a real user.

- signing test - remove FIXME comments; questions answered.

- helpers.bash - document start_registries(); save a .crt file,
  not .cert; and remove unused stop_registries() - it's too hard
  to do right, and very easy for individual tests to 'podman rm -f'

- run-tests - remove SKOPEO_BINARY definition, it's inconsistent
  with the one in helpers.bash

Signed-off-by: Ed Santiago <santiago@redhat.com>

systemtest/run-tests

@@ -3,9 +3,6 @@
 # run-tests - simple wrapper allowing shortcuts on invocation
 #
 
-# FIXME
-export SKOPEO_BINARY=${SKOPEO_BINARY:-/usr/bin/skopeo}
-
 TEST_DIR=$(dirname $0)
 TESTS=$TEST_DIR