bug#36940: tests slowness and failure after recent Tramp changes

[Paul Eggert]

I'm having trouble with 'make check' after the recent Tramp changes on master. 
First, the Tramp tests are now too slow; they take over 6 minutes on my platform 
(Fedora 30 x86-4, AMD Phenom II X4 910e, default optimization), which is so slow 
that I don't want to run 'make check' while developing, which would be a bad 
habit to get into.

Second, the tramp-test19-directory-files-and-attributes test now fails.

A nit: the output has some weird spacing and log lines.

Attached is a log illustrating the problem.

tramp-log.txt
Description: Text document