test/py: Use raw strings more to avoid deprecation warnings

test/py: Use raw strings more to avoid deprecation warnings

We have two further uses of raw string usage in the test/py codebase
that are used under CI.  The first of which is under the bind test and
is a direct update.  The second of which is to strip VT100 codes from
the match buffer.  While switching this to a raw string is also a direct
update, the comment it notes that problems were encountered on Ubuntu
14.04 (and whatever Python 2 version that was) that required slight
tweaks to the regex.  Replace that now that we're saying Python 3.5 is
the minimum.

Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Simon Glass <sjg@chromium.org> [on sandbox]
Signed-off-by: Tom Rini <trini@konsulko.com>