git-arc: Retain color status messages

Newer versions of archanist have an --ansi option to always include the
ansi colors when doing an arc list (or any command really). Add this to
the arc list that's relevant. Add filter to filter out the 'bolding'
though since that interferes with our parsing. This should restore the
color output after df834e06bbc7.

Fixes: df834e06bbc7
Sponsored by: Netflix
Reviewed by: markj, jhb
Differential Revision: https://reviews.freebsd.org/D43459