Fix error codes in Tramp

Fix error codes in Tramp

* lisp/net/tramp-compat.el (tramp-compat-user-error): New defsubst,
taken from tramp.el.
(tramp-file-missing): New defconst.

* lisp/net/tramp.el (tramp-user-error): Remove it.
(tramp-check-proper-method-and-host)
(tramp-dissect-file-name, tramp-debug-message)
(tramp-handle-shell-command):
* lisp/net/tramp-adb.el (tramp-adb-handle-shell-command):
* lisp/net/tramp-gvfs.el (tramp-gvfs-file-name-handler):
Use `tramp-compat-user-error'.

* lisp/net/tramp.el (tramp-handle-insert-file-contents)
(tramp-handle-load):
* lisp/net/tramp-adb.el (tramp-adb-handle-file-local-copy):
* lisp/net/tramp-gvfs.el (tramp-gvfs-handle-file-local-copy)
* lisp/net/tramp-sh.el (tramp-sh-handle-file-local-copy):
* lisp/net/tramp-smb.el (tramp-smb-handle-file-local-copy):
Use `tramp-file-missing'.  (Bug#24714)

* lisp/net/tramp-sh.el (tramp-sh-handle-add-name-to-file):
* lisp/net/tramp-smb.el (tramp-smb-handle-make-symbolic-link):
Use `file-already-exists'.