* automated/tramp-tests.el (tramp--test-enabled): Move connection

* automated/tramp-tests.el (tramp--test-enabled): Move connection
cleanup into this function.  Remove respective code from all test cases.
(tramp--instrument-test-case): Declare `indent' and `debug'.
Handle other errors as well.
(tramp-test14-delete-directory): Check for `file-error' error.
(tramp-test15-copy-directory): Ignore return value of
`copy-directory'.  It's too much hassle to handle it for tramp-adb.el.
(tramp-test19-directory-files-and-attributes): Take care of
timestamp of "../".
(tramp-test20-file-modes, tramp-test27-start-file-process)
(tramp-test28-shell-command): Skip for tramp-adb.el.
(tramp-test21-file-links): `file-truename' shall preserve trailing
link of directories.
(tramp-test22-file-times): Skip if `set-file-times' returns nil.
(tramp-test26-process-file, tramp-test28-shell-command): Let-bind
`kill-buffer-query-functions' to nil.
(tramp-test28-shell-command): Run `async-shell-command' with timeouts.