Don't stack overlays in test-suite

Rather than using the root overlay mount in the rpmtests container as
our lowerdir for per test mounts, just use the original lowerdir from
the host.

This eliminates the extra level of indirection and enables us to use a
podman image mount as the lowerdir (to be done later) as otherwise we
would hit the kernel's limit for maximum fs stacking depth of 2.

Keep the podman backend as is (using "/"), we'll remove it soon anyway.

No functional change.

tests/atlocal.in

@@ -1,13 +1,12 @@
-RPMTREE=/
-
 RPMLIBDIR="@CMAKE_INSTALL_FULL_LIBDIR@"
 export RPMLIBDIR
 
 HAVE_UNSHARE=@HAVE_UNSHARE@
 PYTHON=@PYTHON@
 PGP=@PGP@
 
-RPMTEST="$RPMTREE"
+RPMTREE=${RPMTREE:-/}
+RPMTEST=/
 RPMDATA="/data/"
 
 RPM_CONFIGDIR_PATH="@RPM_CONFIGDIR@"

tests/mktree.fedora

@@ -184,7 +184,7 @@ case $CMD in
     ;;
     check)
         mount_tree
-        snapshot exec --tmpfs /tmp --bind $PWD $PWD \
+        snapshot exec --tmpfs /tmp --bind $PWD $PWD --setenv RPMTREE $RPMTREE \
                       sh -c 'cd '$PWD' && exec ./rpmtests "$@"' rpmtests "$@"
     ;;
     reset)

tests/mktree.podman

@@ -42,7 +42,7 @@ case $CMD in
         esac
         $PODMAN run --privileged -it --rm --read-only --tmpfs /tmp \
                     -v /srv --workdir /srv -e ROOTLESS=$ROOTLESS \
-                    $OPTS $IMAGE mktree check "$@"
+                    --env RPMTREE=/ $OPTS $IMAGE mktree check "$@"
     ;;
     reset)
         $PODMAN stop $NAME >/dev/null &&