Refactor tramp-*-process-file functions

Refactor tramp-*-process-file functions

* lisp/net/tramp-adb.el (tramp-adb-handle-make-process):
* lisp/net/tramp-sh.el (tramp-sh-handle-make-process): Don't compute
process name, this is done in `tramp-skeleton-make-process'.

* lisp/net/tramp-adb.el (tramp-adb-handle-process-file):
* lisp/net/tramp-sh.el (tramp-sh-handle-process-file):
* lisp/net/tramp-sshfs.el (tramp-sshfs-handle-process-file):
Use `tramp-skeleton-process-file'.

* lisp/net/tramp.el (tramp-get-unique-process-name): New defun.
(tramp-skeleton-make-process): Use it.
(tramp-skeleton-process-file): New defmacro.