add a podman-compose command

**podman compose** is a thin wrapper around an external compose provider
such as docker-compose or podman-compose.  This means that `podman
compose` is executing another tool that implements the compose
functionality but sets up the environment in a way to let the compose
provider communicate transparently with the local Podman socket.  The
specified options as well the command and argument are passed directly
to the compose provider.

The default compose providers are `docker-compose` and `podman-compose`.
If installed, `docker-compose` takes precedence since it is the original
implementation of the Compose specification and is widely used on the
supported platforms (i.e., Linux, Mac OS, Windows).

If you want to change the default behavior or have a custom installation
path for your provider of choice, please change the `compose_provider`
field in `containers.conf(5)`.  You may also set the
`PODMAN_COMPOSE_PROVIDER` environment variable.

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

test/compose/test-compose

@@ -276,11 +276,12 @@ done
 # When rootless use a socket path accessible by the rootless user
 if is_rootless; then
     DOCKER_SOCK="$WORKDIR/docker.sock"
-    DOCKER_HOST="unix://$DOCKER_SOCK"
-    # export DOCKER_HOST docker-compose will use it
-    export DOCKER_HOST
 fi
 
+# export DOCKER_HOST docker-compose will use it
+DOCKER_HOST="unix://$DOCKER_SOCK"
+export DOCKER_HOST
+
 # Identify the tests to run. If called with args, use those as globs.
 tests_to_run=()
 if [ -n "$*" ]; then
@@ -331,12 +332,12 @@ for t in "${tests_to_run[@]}"; do
             trap '. teardown.sh' 0
         fi
 
-        docker-compose up -d     &> $logfile
+        podman compose up -d     &> $logfile
         docker_compose_rc=$?
         if [[ $docker_compose_rc -ne 0 ]]; then
             _show_ok 0 "$testname - up" "[ok]" "status=$docker_compose_rc"
             sed -e 's/^/#  /' <$logfile
-            docker-compose down >>$logfile 2>&1      # No status check here
+            podman compose down >>$logfile 2>&1      # No status check here
             exit 1
         fi
         _show_ok 1 "$testname - up"
@@ -354,7 +355,7 @@ for t in "${tests_to_run[@]}"; do
         fi
 
         # Done. Clean up.
-        docker-compose down     &>> $logfile
+        podman compose down     &>> $logfile
         rc=$?
         if [[ $rc -eq 0 ]]; then
             _show_ok 1 "$testname - down"