Since commit fe6da2fe, "auto" color is
supported in OOXML import.

Since ODF doesn't support "auto" color as border color, just convert
"auto" border color to black on import, like is done in GetLineIndex
in ww8par6.cxx.

Incidentally, this also fixes a problem in RTF import, where we used to
import black borders ("\red0\green0\blue0;" entries in color table) as
0x000001 ("\red0\green0\blue1;") - see fixed tests in rtfexport2.cxx.

Change-Id: I4f5e720d215b51c8a43dc7c58f338741bd608efc
Reviewed-on: https://gerrit.libreoffice.org/51519Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>