test/system: fix borken pasta interface name checks

The tests didn't check anything actually because default_ifname requires
an ip version argument to work. Thus pasta_iface was empty, add new
checks to prevent this kind of error again.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

test/system/250-systemd.bats

@@ -319,7 +319,8 @@ LISTEN_FDNAMES=listen_fdnames" | sort)
     # stop systemd container
     service_cleanup
 
-    pasta_iface=$(default_ifname)
+    pasta_iface=$(default_ifname 4)
+    assert "$pasta_iface" != "" "pasta_iface is set"
 
     # now check that the rootless netns slirp4netns process is still alive and working
     run_podman unshare --rootless-netns ip addr

test/system/505-networking-pasta.bats

@@ -784,7 +784,8 @@ EOF
 @test "Podman unshare --rootless-netns with Pasta" {
     skip_if_remote "unshare is local-only"
 
-    pasta_iface=$(default_ifname)
+    pasta_iface=$(default_ifname 4)
+    assert "$pasta_iface" != "" "pasta_iface is set"
 
     # First let's force a setup error by making pasta be "false".
     ln -s /usr/bin/false $PODMAN_TMPDIR/pasta