Use podman in gating tests

Nothing complicated, just a very simple 'run' command.
Currently fails, which is good, it means this test
would have caught today's crisis[1]. Unfortunately
it fails with no useful info whatsoever: the test
result simply shows ERROR. I'm not sure there's much
I can do about this, since podman itself is silent
on the failure. (It'd be nice if gating tests at least
showed us the exit status).

 [1]  https://github.com/containers/container-selinux/issues/169

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

tests/tests.yml

@@ -6,8 +6,11 @@
     required_packages:
     - policycoreutils
     - container-selinux
+    - podman
     tests:
     - is-module-installed:
         run: semodule --list=full | grep container
     - can-rebuild-policy:
         run: semodule -B
+    - can-run-podman:
+        run: podman run --rm quay.io/libpod/testimage:20210610 cat -v /proc/self/attr/current