[haproxy] anchor; make sure configuration is flushed before rename

The pattern:

  create, write, close, rename

is *not* robust in many circumstances.  The data blocks from the write
are not always flushed/persisted before the rename (metadata) changes
meaning you can end up where the replacement file is corrupted
(usually has 0 bytes at the end).

Change-Id: Icdd2bb6f20330e5e94b3081f0d0b8a74417f60d4

charts/haproxy/templates/bin/_anchor.tpl

@@ -134,6 +134,8 @@ install_config() {
               echo Replacing HAProxy config file "$HAPROXY_CONF" with:
               cat "$NEXT_HAPROXY_CONF"
               echo
+              # ensure data blocks are flushed before rename
+              sync
               mv "$NEXT_HAPROXY_CONF" "$HAPROXY_CONF"
             else
               echo "New config failed validation, refusing to replace."