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
failed #6802


failed #6803


Name Stage Failure
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
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