More Tramp optional methods

More Tramp optional methods

* doc/misc/tramp.texi (Inline methods) <krlogin, ksu>:
(External methods) <fcp, nc>: These are optional methods.

* etc/NEWS: Mention more optional Tramp methods.

* lisp/net/tramp-androidsu.el (tramp-enable-androidsu-method):
Use proper regexp for `tramp-default-user-alist'.

* lisp/net/tramp-sh.el (tramp-enable-nc-method)
(tramp-enable-ksu-method, tramp-enable-krlogin-method)
(tramp-enable-fcp-method): New defuns.  Move respective
configurations there.

* lisp/net/tramp.el (tramp-enable-method): Implement completion
for interactive use.

* test/lisp/net/tramp-tests.el (tramp-test03-file-name-defaults)
(tramp-test03-file-name-host-rules): Extend tests.