Ensure that the DF endpoint updated volume refcount

The field was already exposed already in the `system df` output
so this just required a bit of plumbing and testing.

As part of this, fix `podman systemd df` volume in-use logic.
Previously, volumes were only considered to be in use if the
container using them was running. This does not match Docker's
behavior, where a volume is considered in use as long as a
container exists that uses the volume, even if said container is
not running.

Fixes #15720

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

test/apiv2/45-system.at

@@ -25,6 +25,24 @@ t GET system/df 200 '.Volumes[0].Name=foo1'
 
 t GET libpod/system/df 200 '.Volumes[0].VolumeName=foo1'
 
+# Verify that no containers reference the volume
+t GET system/df 200 '.Volumes[0].UsageData.RefCount=0'
+
+# Make a container using the volume
+podman pull $IMAGE &>/dev/null
+t POST containers/create Image=$IMAGE Volumes='{"/test":{}}' HostConfig='{"Binds":["foo1:/test"]}' 201 \
+  .Id~[0-9a-f]\\{64\\}
+cid=$(jq -r '.Id' <<<"$output")
+
+# Verify that one container references the volume
+t GET system/df 200 '.Volumes[0].UsageData.RefCount=1'
+
+# Remove the container
+t DELETE containers/$cid?v=true 204
+
+# Verify that no containers reference the volume
+t GET system/df 200 '.Volumes[0].UsageData.RefCount=0'
+
 # Create two more volumes to test pruneing
 t POST libpod/volumes/create \
   Name=foo2 \

test/system/320-system-df.bats

@@ -27,7 +27,7 @@ function teardown() {
     run_podman system df --format '{{ .Type }}:{{ .Total }}:{{ .Active }}'
     is "${lines[0]}" "Images:1:1"        "system df : Images line"
     is "${lines[1]}" "Containers:2:1"    "system df : Containers line"
-    is "${lines[2]}" "Local Volumes:2:1" "system df : Volumes line"
+    is "${lines[2]}" "Local Volumes:2:2" "system df : Volumes line"
 
     # Try -v. (Grrr. No way to specify individual formats)
     #