Fix preinstallimages in containers (#1031)

* preinstall_image(): Refactor tar and bsdtar excludes into a shared variable

* preinstall_image(): Avoid extracting special files under /dev, /proc, /run and /sys in podman containers

Rootless containers do not have sufficient capabilities to create such special files.
Also, these directories are usually tmpfs mounts so we're not using the original content anyway.

init_buildsystem

@@ -279,11 +279,19 @@ preinstall_image() {
     check_exit
     echo "unpacking preinstall image${2:+ $2}"
     preinstall_setup
+
+    TAR_EXCLUDES="--exclude .build --exclude .init_b_cache"
+
+    if [ -f "/run/.containerenv" ]; then
+        # we're running in a podman container and we probably don't have sufficient capabilities to create special files
+        TAR_EXCLUDES="$TAR_EXCLUDES --exclude dev/* --exclude proc/* --exclude run/* --exclude sys/*"
+    fi
+
     if test -x /usr/bin/bsdtar ; then
-	TAR="/usr/bin/bsdtar --exclude .build --exclude .init_b_cache -P --chroot --numeric-owner -x"
+	TAR="/usr/bin/bsdtar $TAR_EXCLUDES -P --chroot --numeric-owner -x"
     else
 	unsafe_preinstall_check
-	TAR="tar --exclude .build --exclude .init_b_cache -x"
+	TAR="tar $TAR_EXCLUDES -x"
     fi
     if ! $TAR -f "$BUILD_INIT_CACHE/rpms/$1" ; then
 	echo "ERROR: unpack failed."