bug#33781: tramp tests abort on hydra

[Glenn Morris]

On further poking around, I think the issue might be that remote PATH is
getting truncated to ~ 4096 characters, which happens to lose sed.

At least, this is what I seem to see if I add

echo \$PATH > /tmp/FOO

to the start of the shell command in
tramp-do-directory-files-and-attributes-with-stat.