Continue implementation of tramp-crypt.el

Continue implementation of tramp-crypt.el

* lisp/net/tramp-crypt.el (tramp-crypt-do-encrypt-or-decrypt-file):
Add leading "/" to infile.
(tramp-crypt-add-directory): Fix docstring.  Expand NAME.
(tramp-crypt-remove-directory)
(tramp-crypt-handle-file-name-all-completions)
(tramp-crypt-handle-set-file-times): New defuns.
(tramp-crypt-handle-file-executable-p)
(tramp-crypt-handle-file-readable-p)
(tramp-crypt-handle-file-system-info)
(tramp-crypt-handle-set-file-modes): Fix implementation.

* test/lisp/net/tramp-tests.el: Adapt call convention
for (tramp--test-crypt-p).