Tramp code cleanup

Tramp code cleanup

* lisp/net/tramp-sh.el (tramp-methods) <telnet, nc>:
Reintroduce "%n" marker.
(tramp-maybe-open-connection): Handle it.

* lisp/net/tramp.el (tramp-prefix-regexp):
* lisp/net/tramp-smb.el (tramp-smb-options): Fix docstring.

* lisp/net/tramp*.el: Fix typos.  Remove trailing space from
`yes-or-no-p' and `y-or-n-p' prompts.

* test/lisp/net/tramp-tests.el (tramp--test-telnet-p): New defun.
(tramp-test29-start-file-process, tramp-test30-make-process)
(tramp-test35-remote-path, tramp-test44-asynchronous-requests):
Adapt tests.