Fix Tramp portability issues

* lisp/net/tramp-sh.el (tramp-set-remote-path): Replace "echo -n" by
"printf", it isn't portable.

* test/lisp/net/tramp-tests.el (tramp-test33-environment-variables)
(tramp-test33-environment-variables-and-port-numbers): Do not use
"echo -n", it isn't portable.
(tramp--test-utf8): Filter out not displayable characters.
2 jobs for master in 61 minutes and 41 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
failed #6802
test-all

01:01:41

failed #6803
test-filenotify-gio

00:00:32

 
Name Stage Failure
failed
test-all Test
Makefile:318: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:293: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:959: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1
failed
test-filenotify-gio Test
error: cannot lock ref 'refs/remotes/origin/master': Unable to create '/builds/emacs/emacs/.git/refs/remotes/origin/master.lock': File exists.

Another git process seems to be running in this repository, e.g.
an editor opened by 'git commit'. Please make sure all processes
are terminated then try again. If it still fails, a git process
may have crashed in this repository earlier:
remove the file manually to continue.
fatal: failed to run reflog
ERROR: Job failed: exit code 1