Fix multibyte chars of file names in tramp-adb.el

Fix multibyte chars of file names in tramp-adb.el

* lisp/net/tramp-adb.el (tramp-adb-execute-adb-command): Revert return
value meaning.  Insert the result into the connection buffer.
(tramp-adb-handle-file-local-copy)
(tramp-adb-handle-write-region, tramp-adb-handle-copy-file)
(tramp-adb-get-device): Adapt calls.
(tramp-adb-send-command): Use "adb shell ..." in case the command
contains multibyte chars.

* test/lisp/net/tramp-tests.el (tramp--test-utf8): Extend test.