main/dosfstools: install binaries to /sbin
dosfstools installed programs in /usr/sbin which overlap with what busybox provides in /sbin (mkfs.vfat, mkdosfs).
/sbin has priority over /usr/sbin on alpine and there is no mechanism to remove overlapping commands in such case, so change dosfstools to install in /sbin directly instead:
- installing dosfstools will overwrite busybox-provided symlinks
- removing dosfstools will run busybox trigger and restore the symlink
- upgrading busybox itself does not mess with these links either
(the obvious downside is if anyone had hardcoded /usr/sbin/xx paths in their scripts, these will stop working...)
Fixes #13194 (closed).