tidy stx/downloads directory

$MY_REPO/stx/downloads contains links to tarballs and other files
relevant to the build.  It is populated by populate_downloads.sh.
On subsequent runs, new links might be added, but old links are
not cleaned up.

Adopt the convention used by generate-centos-repo.sh of moving
the old content under a timestamp backup directory, leaving
an empty directory to re-populate.

Closes-bug: 1908297
Signed-off-by: Scott Little <scott.little@windriver.com>
Change-Id: Ib6c8b782db6c369cb00e8fe8c64be099d7a5d238

toCOPY/generate-centos-repo.sh

@@ -183,13 +183,13 @@ if [ ! -d "${dest_dir}" ]; then
 fi
 
 for t in "Binary" "Source" ; do
-    target_dir=${dest_dir}/$t
-    if [ ! -d "$target_dir" ]; then
-        mkdir -p "$target_dir"
-    else
-        mv -f "$target_dir" "$target_dir-backup-$timestamp"
-        mkdir -p "$target_dir"
+    target_dir=${dest_dir}/${t}
+
+    if [ -d "${target_dir}" ]; then
+        mv -f "${target_dir}" "${target_dir}-backup-${timestamp}"
     fi
+
+    mkdir -p "${target_dir}"
 done
 
 #

toCOPY/populate_downloads.sh

@@ -91,7 +91,12 @@ if [ -f  ${extra_downloads_lst} ]; then
 fi
 
 
-mkdir -p ${MY_REPO}/stx/downloads
+if [ -d "${downloads_dir}" ]; then
+    timestamp="$(date +%F_%H%M)"
+    mv -f "${downloads_dir}" "${downloads_dir}-backup-${timestamp}"
+fi
+
+mkdir -p ${downloads_dir}
 
 grep -v "^#" ${tarball_lst} | while read x; do
     if [ -z "$x" ]; then