utils.py: Make select_latest_patches treat /srv/patches/next as latest
Changed select_latest_patches to filter candidate directories using
parse_wmf_version (which handles versions such as "next").
Previously it would only consider x.yy.z-wmf.w style versions.
This means that if /srv/patches/next exists, it will be used by
scap prep as the source to populate /srv/patches/<version>. This
is the naturally correct thing to do for T398873 and is also the
correct behavior according to the discussion in T295925.
Edited by Ahmon Dancy